Compute the ventilation rate of any room: ACH from airflow and room dimensions, required CFM for a target ACH, room volume, and typical ACH ranges by room type — all calculated instantly in your browser.
Tip: pick a target from the reference table (tab 4) — clicking a row fills it here automatically.
Typical design ranges compiled from engineering references — not code requirements. Click any row to use its midpoint as your target in tab 2.
| Room type | Typical ACH range | Source |
|---|---|---|
| Bedroom | 2 - 4 | Typical design guidance; code floor is ASHRAE 62.2 whole-home minimum 0.35 ACH |
| Bathroom | 3 - 8 | DIN 1946 |
| Kitchen | 15 - 60 | Engineering Toolbox; residential at the lower end |
| Laboratory | 6 - 15 | DIN 1946; lab systems are engineer-designed |
| Computer / server room | 15 - 20 | Engineering Toolbox (Computer Rooms) |
| Living areas (residences) | 1 - 2 | Engineering Toolbox (Residences) |
| Office | 3 - 4 | Engineering Toolbox (public 3, private 4) |
| Classroom | 4 - 12 | Engineering Toolbox (School Classrooms) |
| Restaurant dining | 8 - 12 | Engineering Toolbox (Restaurants) |
| Laundry | 10 - 15 | Engineering Toolbox (Laundries) |
Sources: Engineering Toolbox, Recommended Air Change Rates for Different Room Types; Axair, Air Change per Hour Document (DIN 1946 part 2); Code floor for homes: ASHRAE 62.2-2016 requires at least 0.35 ACH of whole-building ventilation (and not less than 15 CFM per person). Always check your local building code.
A 10 × 12 × 8 ft bedroom has a volume of 960 ft³. With a 100 CFM supply grille the ventilation rate is ACH = 100 × 60 / 960 = 6.25, so the room air is fully replaced about every 9.6 minutes. To hit a target of 6 ACH in the same room you would need 6 × 960 / 60 = 96 CFM (163.1 m³/h).
ACH measures how many times the entire air volume of a room is replaced in one hour. An ACH of 6 means the full room volume passes through the ventilation system six times per hour, which is about one complete change every 10 minutes.
ACH = CFM x 60 / room volume in cubic feet. Multiply the supply airflow in cubic feet per minute by 60 to get cubic feet per hour, then divide by the room volume. For metric inputs use ACH = airflow in m3/h divided by room volume in m3.
Room volume = 10 x 12 x 8 = 960 ft3. ACH = 100 x 60 / 960 = 6.25. One full air change takes 60 / 6.25 = 9.6 minutes.
CFM = ACH x room volume / 60. For 6 ACH in a 960 ft3 room: 6 x 960 / 60 = 96 CFM, which equals 163.1 m3/h.
Typical design guidance is 2 to 4 ACH for bedrooms. As a code floor, ASHRAE 62.2-2016 requires homes to receive at least 0.35 ACH of whole-building ventilation, and not less than 15 CFM per person.
The typical design range for bathrooms is 3 to 8 ACH (DIN 1946). Bathrooms are moisture sources, so local exhaust sized for the actual fixtures usually governs over the ACH rule of thumb.
The typical range is 15 to 60 ACH (Engineering Toolbox). Residential kitchens sit at the lower end of that range and commercial kitchens at the higher end, because cooking heat, grease, and odors drive the requirement.
The typical design range is 6 to 15 ACH (DIN 1946). Laboratory ventilation is engineer-designed around fume hoods and chemical safety requirements, so treat the range as a starting point for discussion, not a specification.
The typical range is 15 to 20 ACH (Engineering Toolbox, listed as Computer Rooms). Server rooms are driven by heat load rather than occupancy, so confirm cooling capacity separately from the ventilation rate.
No. An ACH figure on an air purifier box describes how often the purifier filters the room air for particles; it does not bring in fresh outdoor air. Ventilation ACH, which this calculator measures, is the rate of fresh-air exchange with the outside. For purifier sizing by CADR, use our air purifier room size calculator instead.
Swamp (evaporative) coolers are sized by CFM per square foot of floor area for cooling, not by air changes per hour. Use our swamp cooler size calculator for evaporative cooling; use this tool when you need the ventilation rate itself.
Two equivalent ways: convert the room volume to cubic feet by multiplying m3 by 35.3147 and use ACH = CFM x 60 / ft3, or stay fully metric with ACH = airflow in m3/h divided by volume in m3. For reference, 100 CFM equals 169.9 m3/h.
Divide 60 by the ACH. At 6.25 ACH one full change takes 9.6 minutes; at 20 ACH it takes 3 minutes. This assumes well-mixed air; real rooms have corners and dead spots where air lingers longer.
Not necessarily. Beyond the target range for the room type you pay more in fan energy and noise, and high air velocity causes uncomfortable drafts. Balance the ACH target with good filtration and controlling pollutants at their source instead of chasing the highest number.
No. The reference table shows typical design ranges compiled from engineering references; they are not code requirements. Always check your local building code and the ASHRAE 62.1 (commercial) or 62.2 (residential) provisions that apply to your project.
Free tool by NRTechStudio
Explore similar general tools and calculators. 100% free, accurate, and runs completely in your browser without sign-up.
2 taps, no typing needed — diagnostics are sent automatically.