What Size Air Purifier Do I Need?
Get instant CADR recommendations with our free calculator. Simply enter your room details for personalized sizing guidance.
Quick Answer
Rule of thumb: Divide your room's square footage by 1.5 to get minimum CADR needed. For example, a 300 sq ft room needs at least 200 CFM CADR.
Free Air Purifier Size Calculator
Enter your room details below to get instant CADR recommendations. Our calculator considers room volume, type, and air quality needs.
Air Purifier Room Size Calculator
Enter your room dimensions and type to get an instant CADR recommendation. Our calculator considers room-specific factors to find the perfect air purifier for your space.
Room Details
Standard ceiling height - most air purifiers are optimized for this range.
Bedrooms benefit from 10% higher CADR for better sleep quality and allergen control.
Recommended CADR
Ideal for medium-sized air purifiers. Many popular models are designed for this range.
Room Coverage Visualization
Top 3 Recommendations for Your 300 sq ft Bedroom
Real-World Room Size Calculator Examples
See how our calculator determines the perfect CADR for different room types and sizes
Master Bedroom
Needs 120 CFM CADR minimum. Bedroom multiplier ensures quiet, restful sleep while maintaining clean air throughout the night.
Open Living Room
Needs 250 CFM CADR minimum. Higher activity levels and foot traffic require stronger purification to maintain air quality.
Home Office
Needs 75 CFM CADR minimum. Compact units work well for focused productivity while maintaining healthy indoor air quality.
Large Kitchen
Needs 405 CFM CADR minimum. Kitchen multiplier accounts for cooking odors, grease particles, and higher pollution from meal preparation.
Finished Basement
Needs 448 CFM CADR minimum. Basement multiplier addresses humidity, musty odors, and potential mold issues common in below-grade spaces.
Calculate Your Room
Every room is unique. Get precise CADR requirements based on your exact square footage, ceiling height, and room type.
How to Use This Calculator
Our Room Size Calculator makes it easy to find the perfect air purifier for your space. Simply enter your room details and get instant CADR recommendations based on square footage, ceiling height, and room-specific factors.
1Calculate Your Room Size
Measure the length and width of your room in feet, then multiply to get square footage. For example: 15 ft × 12 ft = 180 sq ft. Use the slider or type directly for precise input.
2Select Ceiling Height
Choose your ceiling height from the dropdown. Standard residential ceilings are 8 feet, but newer homes often have 9-10 feet. Higher ceilings mean more air volume to clean.
3Choose Room Type
Select your room type to apply the appropriate CADR multiplier. Different rooms have varying air quality needs:
- • Bedrooms: Clean air for quality sleep
- • Living rooms: Higher traffic, more particles
- • Kitchens: Cooking odors and grease particles
- • Offices: Dust from electronics and paper
- • Basements: Humidity and potential mold
4Review Recommendations
Get your recommended CADR with a suggested range for flexibility. The calculator also shows air changes per hour, room volume, and efficiency ratings to help you understand the results.
Understanding Your Results
The calculator provides several key metrics to help you choose the right air purifier. Here's what each number means and how to use this information when shopping for your ideal air cleaning solution.
Recommended CADR
This is your target Clean Air Delivery Rate in CFM (cubic feet per minute). It's calculated based on your room volume, ceiling height, and room type. Look for air purifiers with CADR ratings at or above this number.
Example: For a 300 sq ft bedroom with 8 ft ceilings, you need about 200 CFM CADR. A 250 CFM unit would work perfectly and provide extra capacity.
CADR Range
We provide a range (minimum to maximum) to give you flexibility. Choose the minimum for basic cleaning, middle range for standard use, or maximum for allergies, pets, or heavy pollution.
Flexibility: Higher CADR units can run on lower speeds for quieter operation while maintaining effectiveness.
Air Changes per Hour (ACH)
This shows how many times your room's air gets completely filtered each hour. Higher numbers mean faster, more thorough cleaning:
Room Type Multipliers Explained
- • Bedrooms: 1.0x (baseline)
- • Living rooms: 1.2x (more activity)
- • Offices: 1.1x (electronics, paper dust)
- • Kitchens: 1.5x (cooking particles)
- • Basements: 1.3x (humidity, mold risk)
Understanding Room Size and CADR Relationship
The relationship between room size and CADR (Clean Air Delivery Rate) is fundamental to effective air purification. Understanding this connection helps you choose the right air purifier size and avoid common sizing mistakes.
The Basic Formula
CADR needed = (Room Volume ÷ 60) × Target ACH. For example, a 2,400 cubic foot room targeting 5 ACH needs 200 CFM CADR minimum.
Why Size Matters
Larger rooms contain more air that needs filtering. An undersized air purifier will run constantly at maximum speed, creating noise while struggling to maintain clean air.
Common Mistakes
Many people buy air purifiers based on "room coverage" claims without considering ceiling height or room type. Marketing square footage can be misleading.
CADR Requirements by Room Size
| Room Size | 8 ft Ceiling | 9 ft Ceiling | 10 ft Ceiling | Recommended Units |
|---|---|---|---|---|
| 150 sq ft | 100-150 CFM | 115-170 CFM | 125-190 CFM | Compact desktop units |
| 300 sq ft | 200-300 CFM | 225-340 CFM | 250-375 CFM | Medium room units |
| 500 sq ft | 335-500 CFM | 375-565 CFM | 415-625 CFM | Large room units |
| 750 sq ft | 500-750 CFM | 565-845 CFM | 625-940 CFM | Multiple units or industrial |
Special Considerations
When to Size Up:
- • Open floor plans or connected rooms
- • Heavy pollution sources (smoking, cooking)
- • Allergies, asthma, or respiratory conditions
- • Pets that shed or produce dander
Multiple Unit Strategy:
- • Rooms over 600 sq ft benefit from 2 smaller units
- • Better air circulation and coverage
- • Redundancy if one unit fails
- • Can run at lower speeds for quieter operation
Example Calculations for Different Room Scenarios
See how our room size calculator works with real-world examples. Each scenario shows different considerations and explains why specific CADR ratings are recommended.
Small Bedroom (12' × 10' × 8')
Scenario Details:
- • Room: 120 sq ft (12' × 10')
- • Ceiling: 8 feet (standard)
- • Volume: 960 cubic feet
- • Usage: Master bedroom for allergic adult
- • Goal: Clean air for better sleep
Calculation & Result:
Basic CADR: 120 × 0.67 = 80 CFM
Allergy CADR: 120 × 1.0 = 120 CFM
Recommended: 80-120 CFM
✓ Compact desktop unit sufficient
Why this works: Small bedrooms need moderate air cleaning focused on nighttime pollutants. A 100 CFM unit provides 6+ air changes per hour, ideal for allergy relief without excessive noise.
Living Room with Pets (20' × 15' × 9')
Scenario Details:
- • Room: 300 sq ft (20' × 15')
- • Ceiling: 9 feet (high ceiling)
- • Volume: 2,700 cubic feet
- • Usage: Family room with 2 cats
- • Goal: Control pet dander and odors
Calculation & Result:
Basic CADR: 300 × 0.67 = 200 CFM
Pet CADR: 300 × 1.25 = 375 CFM
Recommended: 300-375 CFM
✓ Large room unit or 2 medium units
Why this works: Pet dander requires higher air turnover rates. The 375 CFM recommendation provides 5+ air changes per hour, effectively capturing dander and controlling odors from litter boxes.
Open Floor Plan Kitchen/Living (25' × 18' × 10')
Scenario Details:
- • Room: 450 sq ft (25' × 18')
- • Ceiling: 10 feet (vaulted)
- • Volume: 4,500 cubic feet
- • Usage: Combined kitchen and living area
- • Goal: Handle cooking particles and general air quality
Calculation & Result:
Basic CADR: 450 × 0.67 = 300 CFM
Cooking CADR: 450 × 1.5 = 675 CFM
Recommended: 500-675 CFM
✓ Multiple units strategy recommended
Why this works: Open floor plans and cooking areas need higher capacity. Consider placing one 350 CFM unit near the kitchen and another 300 CFM unit in the living area for optimal coverage and air circulation.
Home Office (14' × 12' × 8')
Scenario Details:
- • Room: 168 sq ft (14' × 12')
- • Ceiling: 8 feet (standard)
- • Volume: 1,344 cubic feet
- • Usage: 8+ hours daily workspace
- • Goal: Maintain concentration and air quality
Calculation & Result:
Basic CADR: 168 × 0.67 = 112 CFM
Premium CADR: 168 × 1.0 = 168 CFM
Recommended: 110-170 CFM
✓ Medium desktop unit with quiet operation
Why this works: Home offices need consistent air quality without noise distraction. A 150 CFM unit provides 6.7 air changes per hour while maintaining whisper-quiet operation on medium settings.
Large Master Bedroom with Ensuite (18' × 16' × 9')
Scenario Details:
- • Room: 288 sq ft (18' × 16')
- • Ceiling: 9 feet (high ceiling)
- • Volume: 2,592 cubic feet
- • Usage: Master suite with bathroom connection
- • Goal: Premium air quality for sleep and health
Calculation & Result:
Basic CADR: 288 × 0.67 = 193 CFM
Premium CADR: 288 × 1.25 = 360 CFM
Recommended: 250-360 CFM
✓ Large bedroom unit with smart features
Why this works: Large bedrooms benefit from higher-capacity units that can operate on low speeds. A 300 CFM unit provides excellent air quality while running virtually silent during sleep hours.
Key Takeaways from These Examples
Room Purpose Matters
Bedrooms need quieter operation, kitchens need higher capacity for particles, and offices need consistent air quality.
Ceiling Height Impact
Higher ceilings significantly increase room volume, requiring proportionally higher CADR ratings for effective air cleaning.
Special Considerations
Pets, cooking, allergies, and open floor plans all require sizing up your air purifier for optimal performance.
Frequently Asked Questions
Get answers to the most common questions about room size calculations, CADR requirements, and air purifier selection.
What if my room is an irregular shape or has odd dimensions?
For irregular rooms, calculate the total floor area by breaking it into rectangles and adding them together. The calculator uses total square footage, so shape doesn't directly affect the CADR recommendation.
L-shaped rooms: Measure each section separately (e.g., 12'×15' living area + 8'×10' dining nook = 180 + 80 = 260 sq ft total).
Rooms with alcoves: Include all floor space where air needs to be cleaned. Consider placing the air purifier centrally for better circulation in irregular spaces.
Should I choose the minimum or maximum recommended CADR range?
Choose based on your specific air quality needs and tolerance for noise:
- Minimum CADR: Basic air cleaning for healthy individuals in low-pollution environments
- Mid-range CADR: Best for most situations - good cleaning power with reasonable noise levels
- Maximum CADR: Ideal for allergies, asthma, heavy pollution sources, or when you want to run the unit on quieter low speeds
Pro tip: When in doubt, choose higher CADR. You can always run a powerful unit on lower speeds for quieter operation.
Can I use an air purifier with higher CADR than recommended?
Absolutely! Higher CADR is generally better and offers several advantages:
- Faster cleaning: Reaches target air quality more quickly
- Quieter operation: Can run on lower fan speeds while maintaining effectiveness
- Better coverage: More effective for larger or challenging spaces
- Future-proofing: Handles increased pollution or room changes
The only downsides are higher upfront cost and potentially higher energy consumption if run at full speed constantly.
How do open floor plans and connected rooms affect the calculation?
Open floor plans require special consideration because air moves freely between spaces:
- Calculate total area: Include all connected spaces (living room + kitchen + dining area)
- Consider multiple units: For areas over 500 sq ft, two smaller units often work better than one large unit
- Strategic placement: Place the air purifier centrally where air can circulate to all areas
- Account for obstacles: Furniture, walls, and room dividers can impede air circulation
Example: A 600 sq ft open floor plan might benefit from two 300 CFM units rather than one 600 CFM unit for better air circulation.
Why do different room types need different CADR levels?
Different rooms have varying pollution sources, occupancy patterns, and air quality requirements:
High-Pollution Rooms:
- • Kitchens: Cooking particles, grease, odors
- • Basements: Humidity, mold, dust
- • Home offices: Printer particles, long occupancy
Sensitive Rooms:
- • Bedrooms: 6-8 hours of exposure during sleep
- • Nurseries: Developing respiratory systems
- • Living rooms: High family activity and time spent
Match your CADR to both room size and pollution level for optimal air quality.
How accurate does my room measurement need to be?
Room measurements should be reasonably accurate, but perfect precision isn't critical:
- ±6 inches is fine: Small measurement errors won't significantly affect CADR recommendations
- Round to nearest foot: 12'3" can be rounded to 12' for simplicity
- Include major alcoves: Don't ignore significant floor space extensions
- Ceiling height matters more: 8' vs 10' ceilings create a 25% volume difference
Pro tip: When measurements are borderline between size categories, choose the higher CADR for better performance.
What if I have pets, allergies, or smoke in the room?
Special circumstances require higher CADR ratings for effective air cleaning:
Size Up For:
- • Pets: +25-50% CADR for dander and odors
- • Allergies/Asthma: +50% CADR for faster cleaning
- • Smoking: +100% CADR minimum, prefer multiple units
- • Cooking: +50-75% CADR for particles and odors
Filter Considerations:
- • HEPA filters: Essential for allergens and small particles
- • Activated carbon: Needed for odors and gases
- • Pre-filters: Extend HEPA life with pet hair
Remember: our calculator provides baseline recommendations. Add 25-50% CADR for challenging environments.
Is it better to have one large air purifier or multiple smaller ones?
The answer depends on your room size, layout, and budget:
Multiple Smaller Units:
- • Better air circulation and coverage
- • Redundancy if one unit fails
- • Can target specific problem areas
- • Often more cost-effective
- • Ideal for rooms over 400 sq ft
One Large Unit:
- • Simpler maintenance and operation
- • Takes up less floor space
- • Often more energy efficient
- • Better for smaller, single rooms
- • Ideal for rooms under 300 sq ft
Best practice: For large rooms (500+ sq ft), consider two units with 60-70% of the total required CADR each.
How does ceiling height really impact air purifier performance?
Ceiling height directly affects room volume and air circulation patterns:
Volume Impact Examples:
- • 200 sq ft × 8' ceiling = 1,600 cubic feet
- • 200 sq ft × 10' ceiling = 2,000 cubic feet (+25% more air to clean)
- • 200 sq ft × 12' ceiling = 2,400 cubic feet (+50% more air to clean)
Practical implications:
- Higher ceilings need more CADR: More air volume requires proportionally higher cleaning capacity
- Air circulation changes: Tall rooms can develop temperature and air quality stratification
- Placement matters more: Consider ceiling fans or higher unit placement for better mixing
Our calculator automatically adjusts for ceiling height, but rooms over 10 feet may benefit from additional circulation assistance.
What's the difference between CADR ratings for dust, pollen, and smoke?
CADR ratings test three different particle sizes that represent common indoor pollutants:
Dust (0.5-3 μm)
- • Dust mites
- • Fabric fibers
- • General household dust
- • Usually highest CADR
Pollen (5-11 μm)
- • Tree and grass pollen
- • Large allergen particles
- • Pet dander (larger pieces)
- • Easiest to filter
Smoke (0.09-1 μm)
- • Cigarette smoke
- • Cooking particles
- • Fine combustion particles
- • Usually lowest CADR
For room sizing: Use the dust CADR rating as it typically represents the unit's overall performance for most household pollutants. If you have specific concerns about smoke or fine particles, prioritize the smoke CADR rating.
Related Calculators
Specific Room Size Calculators
Jump directly to specialized calculators for common room sizes. Each includes detailed guides, product recommendations, and room-specific optimization tips.
Specialized Calculators
Understanding Air Purifier Sizing
Choosing the right size air purifier is crucial for effective air cleaning. Too small, and it won't clean your air properly. Here's what you need to know.
Why Size Matters More Than You Think
Undersized Air Purifiers
Can't keep up with air pollution, run constantly at maximum speed, create excessive noise, and provide poor air quality results.
Properly Sized Units
Maintain clean air efficiently, operate quietly on medium settings, provide consistent air quality, and last longer with less strain.
Oversized Benefits
Clean air faster, run whisper-quiet on low speeds, handle challenging conditions better, and provide excellent coverage.
The CADR-to-Room Size Formula
Small Rooms
100-250 sq ft
Bedrooms, offices, nurseries
CADR Needed: 67-200 CFM
Compact to medium desktop units
Best for: Personal spaces, quiet operation priority, limited floor space
Medium Rooms
250-500 sq ft
Living rooms, master bedrooms
CADR Needed: 200-400 CFM
Medium to large room units
Best for: Family spaces, moderate to high traffic, pets
Large Rooms
500+ sq ft
Open floor plans, basements
CADR Needed: 400+ CFM
Large units or multiple units
Best for: Open concepts, challenging environments, maximum coverage
5 Common Air Purifier Sizing Mistakes
Avoid these expensive mistakes when choosing your air purifier size. Learning from others' errors can save you money and frustration.
1. Trusting Marketing "Coverage" Claims
Manufacturer coverage claims often assume perfect conditions with low ceilings and minimal pollution.
Solution: Always check actual CADR ratings instead of coverage square footage.
2. Forgetting About Ceiling Height
A 300 sq ft room with 12-foot ceilings has 50% more air volume than one with 8-foot ceilings.
Solution: Always factor in ceiling height when calculating room volume.
3. Ignoring Open Floor Plans
Open floor plans need sizing for the total connected area, not just one section.
Solution: Calculate total square footage of connected spaces or use multiple units.
4. Not Considering Special Conditions
Pets, smoking, cooking, or allergies require 25-100% higher CADR than baseline calculations.
Solution: Add 25-50% CADR for pets/allergies, 50-100% for smoking/heavy cooking.
5. Prioritizing Price Over Performance
Buying an undersized unit to save money results in poor air quality and higher energy costs.
Solution: Invest in proper sizing. A larger unit running on low speed is more efficient.
💡 Pro Tip: When in Doubt, Size Up
It's better to have too much CADR than too little. Oversized units can run on quieter low speeds while maintaining excellent air quality.
What is CADR and Why Does it Matter?
CADR (Clean Air Delivery Rate) is the gold standard for measuring air purifier performance. It tells you how much clean air an air purifier can deliver per minute.
AHAM Verified
CADR ratings are independently tested and verified by the Association of Home Appliance Manufacturers.
Three Ratings
CADR is measured for dust (0.5-3μm), pollen (5-11μm), and smoke (0.09-1μm) particles.
Higher is Better
Higher CADR means faster air cleaning. Match CADR to room size for optimal performance.
CADR Quick Reference
Best for household dust, pet dander, and general particles
Ideal for seasonal allergies and larger allergens
Critical for cooking smoke and fine particles
Pro Tip: Use the dust CADR for general room sizing, but prioritize smoke CADR if you have specific concerns about cooking or fine particles.
Sizing Guide by Room Type
Different rooms have varying air quality needs and pollution sources. Use these specific guidelines for optimal air purifier sizing.
Bedrooms
Sizing Formula
Room area × 0.67 = Minimum CADR
Special Considerations
- • Prioritize quiet operation
- • 6-8 hours of continuous exposure
- • Consider sleep mode features
- • Add 25% for allergies
Example: 300 sq ft bedroom = 200 CFM minimum, 250 CFM for allergies
Living Rooms
Sizing Formula
Room area × 0.8 = Minimum CADR
Special Considerations
- • Higher traffic and activity
- • Multiple occupants
- • Often connected to other rooms
- • Consider smart auto modes
Example: 400 sq ft living room = 320 CFM minimum, 400 CFM recommended
Kitchens
Sizing Formula
Room area × 1.0 = Minimum CADR
Special Considerations
- • Cooking particles and odors
- • Grease and steam
- • Need activated carbon filters
- • Consider placement away from heat
Example: 200 sq ft kitchen = 200 CFM minimum, 300 CFM for heavy cooking
Home Offices
Sizing Formula
Room area × 0.75 = Minimum CADR
Special Considerations
- • Long hours of exposure
- • Printer/electronic particles
- • Need for concentration
- • Prioritize quiet operation
Example: 150 sq ft office = 113 CFM minimum, 150 CFM for all-day use
Basements
Sizing Formula
Room area × 0.87 = Minimum CADR
Special Considerations
- • Humidity and mold concerns
- • Musty odors
- • Poor natural ventilation
- • Consider dehumidifier combo
Example: 500 sq ft basement = 435 CFM minimum, 500+ CFM recommended
Nurseries
Sizing Formula
Room area × 1.0 = Minimum CADR
Special Considerations
- • Developing respiratory systems
- • Maximum quiet operation essential
- • Night light features
- • Safety certifications
Example: 120 sq ft nursery = 120 CFM minimum, prioritize whisper-quiet units
Frequently Asked Questions
Get answers to the most common air purifier sizing questions.
What size air purifier do I need for a 300 sq ft room?
For a 300 sq ft room with 8-foot ceilings, you need an air purifier with 200-300 CFM CADR. Choose the higher end (250-300 CFM) for bedrooms, living rooms, or if you have pets or allergies. Popular models in this range include the Coway Airmega 300S and Levoit Core 400S.
How do I calculate air purifier size?
Calculate air purifier size by: 1) Measuring room area (length × width), 2) Noting ceiling height, 3) Applying room type multiplier (bedrooms 1.0x, living rooms 1.2x, kitchens 1.5x), 4) Using formula: (Room Volume ÷ 60) × Target ACH = Required CADR. Target 5 ACH for most rooms, 6 ACH for nurseries or severe allergies.
Can I use a larger air purifier than recommended?
Absolutely! Using a larger air purifier than recommended is actually beneficial. It cleans air faster, can run on quieter lower speeds while maintaining effectiveness, provides better coverage for challenging conditions, and offers room for future needs. The only downsides are higher upfront cost and potentially higher energy use if run at full speed constantly.
What's the difference between room coverage and CADR?
Room coverage claims from manufacturers often assume ideal conditions (low ceilings, minimal pollution, low air change rates). CADR is the actual measured performance - how much clean air the unit delivers per minute. Always prioritize CADR ratings over coverage claims for accurate sizing. A good rule: CADR × 1.55 = realistic room size coverage.
How does ceiling height affect air purifier sizing?
Ceiling height directly impacts room volume and required CADR. A 200 sq ft room with 10-foot ceilings has 25% more air volume than one with 8-foot ceilings, requiring proportionally more CADR. Our calculator automatically adjusts for this. High ceilings (10+ feet) may also benefit from ceiling fans to improve air circulation.
Should I get one large air purifier or multiple smaller ones?
For rooms under 300 sq ft, one appropriately sized unit works well. For larger spaces (400+ sq ft), two smaller units often provide better coverage than one large unit. Benefits of multiple units include: better air circulation, redundancy if one fails, ability to target specific problem areas, and often more cost-effective than single large units.
Ready to Find Your Perfect Air Purifier?
Use our calculator above to get your exact sizing requirements, then browse our 2025 recommendations for the best units in your size range.
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