Air Change Rate Calculator
Calculate air changes per hour (ACH) for a room from its airflow and dimensions, or solve for the airflow needed to hit a target ACH — SI or US units, checked against common minimum-ventilation ACH guidelines by room type.
Input
SI metric enters room dimensions in metres and airflow in m³/h; US customary uses feet and CFM (cubic feet per minute).
Room
The fan/HVAC system's rated airflow (CFM in US customary, m³/h in SI).
Output
| Metric | Value |
|---|---|
| No data yet | |
| Room type | Typical ACH | |
|---|---|---|
| No data yet | ||
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/air-change-rate-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"calculationMode": "fromAirflow",
"unitSystem": "us",
"roomLength": "12",
"roomWidth": "10",
"roomHeight": "8",
"airflow": "150"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `air-change-rate-calculator` tool (Air Change Rate Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/air-change-rate-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Air Change Rate Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
The Air Change Rate Calculator works out air changes per hour (ACH) — how many times a room's entire air volume is replaced by fresh or conditioned air in one hour — from the room's dimensions and its ventilation system's airflow. It also runs in reverse: given a target ACH, it solves for the airflow a fan or HVAC system needs to deliver. Results are checked against common minimum-ventilation ACH guidelines for a range of room types. It supports SI metric (m³/h, m³, metres) or US customary (CFM, ft³, feet) units.
How to use it
- Choose whether to calculate ACH from airflow or calculate the required airflow from a target ACH.
- Pick your unit system.
- Enter the room's length, width and height.
- Enter the airflow (or the target ACH, depending on the mode).
Results update instantly: the room's volume, its airflow, and its air changes per hour. A reference table then shows where that ACH sits against typical minimum-ventilation guidelines for common room types (bedrooms, kitchens, bathrooms, offices, labs and more), flagging every range it falls within.
What is ACH (air changes per hour)?
Air changes per hour measures ventilation rate as a multiple of the room's own volume:
ACH = (airflow per hour) / (room volume)A CFM (cubic feet per minute) airflow rating is first converted to a per-hour rate (× 60) before dividing by the room's volume in cubic feet; an m³/h rating (the unit European ventilation specs typically use) divides directly into the room's volume in cubic metres. Solving for airflow instead just rearranges the same equation: airflow = ACH × volume (per hour), or airflow = ACH × volume / 60 for a per-minute (CFM) rating.
What ACH should a room have?
Minimum ventilation rates vary widely by use — a bedroom needs far less fresh air turnover than an operating room or a commercial kitchen. The guideline table shows typical published ranges: 2-4 ACH for bedrooms and warehouses, 4-6 for offices, 6-8 for classrooms, 8-15 for bathrooms, 15-20 for kitchens with cooking exhaust, and up to 20-25 for operating rooms. These are general reference ranges, not a substitute for the ventilation code (e.g. ASHRAE 62.1/170) that applies to your specific building and jurisdiction.
Is my data private?
Completely. Every calculation runs entirely in your browser. Nothing you type is uploaded, stored or sent to a server, so you can run as many ventilation checks as you like in total privacy.