What is a good ACH for an office?

ASHRAE recommends 4–10 ACH for standard office spaces. Higher ACH values (8–12) are preferred for open-plan offices with many occupants. Well-designed modern offices often target 6 ACH minimum.

What ACH is required for a hospital room?

Hospital general patient rooms require a minimum of 6 ACH of total air (2 ACH outside air) per ASHRAE 170. Operating rooms require 20 ACH or more. ICUs typically need 6–15 ACH.

How do I convert CFM to ACH?

Use the formula: ACH = (CFM × 60) ÷ Room Volume (ft³). Multiply CFM by 60 to get cubic feet per hour, then divide by the room volume in cubic feet.

What does a higher ACH mean?

A higher ACH means the air in the room is refreshed more frequently, which improves indoor air quality, removes contaminants faster, and dilutes airborne pathogens. However, very high ACH can increase energy costs and cause drafts.

What is a typical ACH for a residential home?

Typical homes have 0.35–1.0 natural ACH (infiltration). ASHRAE 62.2 recommends a minimum of 0.35 ACH or 15 CFM per person for residential spaces with mechanical ventilation.

Can I use this calculator for exhaust fans in bathrooms?

Yes. Bathroom exhaust fans are typically rated in CFM. Enter the bathroom dimensions and the fan's CFM rating to see how many ACH it provides. Most standards recommend 8 ACH minimum for bathrooms.

Room Air Changes Calculator

Enter your room dimensions and airflow rate to instantly calculate air changes per hour (ACH) and see if ventilation meets recommended standards.

Room Dimensions & Airflow

Units:

Length (ft)

Width (ft)

Height (ft)

Airflow Rate (CFM)

Enter the total supply airflow from your HVAC system or fan rating.

Room Type (for reference)

Results

Enter dimensions and airflow, then click Calculate.

Reverse: Required Airflow for Target ACH

Target ACH

Common ACH Benchmarks (ASHRAE / Industry)

Room Type	Min ACH	Max ACH
Office / Conference	4	10
Classroom	4	12
Residential / Bedroom	0.35	1
Bathroom / Restroom	8	15
Commercial Kitchen	15	30
Hospital — General Ward	6	12
Hospital — Operating Room	20	—
Server Room / Data Center	20	60
Laboratory	6	12
Gym / Fitness Area	6	12

Summary

Enter your room dimensions and airflow rate to instantly calculate air changes per hour (ACH) and see if ventilation meets recommended standards.

How it works

Enter the room length, width, and ceiling height using either imperial (ft) or metric (m) units.
Enter the total supply airflow rate in CFM (cubic feet per minute) or m³/h (cubic meters per hour).
The calculator computes room volume and converts all values to consistent units.
ACH is calculated as: ACH = (Airflow Rate × 60) ÷ Room Volume.
Your result is compared against recommended ACH ranges for common room types such as offices, classrooms, and hospitals.

Use cases

Verify that a proposed HVAC system meets ventilation requirements for a new building.
Audit existing ventilation in offices, schools, or healthcare facilities.
Calculate required CFM for a target ACH in a specific room type.
Support indoor air quality assessments and COVID-19 ventilation improvements.
Size exhaust fans for bathrooms, kitchens, and server rooms.
Check compliance with ASHRAE 62.1 or local building code ventilation minimums.
Help mechanical engineers validate ductwork design against room volume.
Educate students and technicians on HVAC fundamentals.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu