CFM to m³/h (the conversion most people want)
Cubic feet per minute (CFM) is the imperial airflow unit; cubic metres per hour (m³/h, often written CMH) is the metric one. To convert CFM to m³/h, multiply by 1.699; to go the other way, divide by 1.699 (or multiply by 0.5886). The factor comes straight from the units: one cubic foot is 0.0283168 m³ and an hour has 60 minutes, so 1 CFM = 0.0283168 × 60 = 1.699 m³/h.
So 400 CFM is about 680 m³/h, and 1000 m³/h is about 589 CFM. The live volume-flow row above does CFM, m³/h, m³/s, L/s, Nm³/h and CFS all at once — no download, no app needed.
CFM, velocity (fpm) and area
People often ask to convert CFM to fpm or fpm to CFM directly, but you cannot — they are different quantities linked by the duct cross-section. Velocity in feet per minute equals airflow divided by area: fpm = CFM / area(ft²), and CFM = fpm × area. The velocity tab solves whichever one you leave out. To find the air velocity for a given duct and airflow, or to size a duct from a target velocity, the duct size calculator goes further and adds friction loss.
CFM to tons and BTU
Airflow and capacity are related by rules of thumb. HVAC systems move about 400 CFM per ton of cooling (range 350–450), so the tons tab divides CFM by 400. Separately, the sensible heat an airstream carries is BTU/h = 1.08 × CFM × ΔT, where ΔT is the temperature change across the coil. Note that a "ton" is 12,000 BTU/h of capacity, which is not the same thing as airflow — the 400 CFM/ton figure is just how much air a typical system pushes per ton.
Compressed air: SCFM, ACFM and hp
Compressed-air flow has its own units that trip people up. SCFM (standard cubic feet per minute) is the flow corrected to standard reference conditions — commonly 14.7 psia, 60 °F, 0% humidity. Think of it as the number on the label. ACFM (actual cubic feet per minute) is the real volumetric flow at your actual pressure and temperature — the number in the field. They match only at standard conditions:
At higher altitude the atmosphere is thinner, so ACFM rises relative to SCFM; at higher gauge pressure the air is compressed into a smaller actual volume, so ACFM falls. The compressed-air tab does this both ways with pressure, temperature and altitude inputs.
Why psi and CFM are not directly convertible
There is no "psi to CFM" formula, and any tool that gives you one is wrong. PSI is pressure — force per unit area — while CFM is flow — volume per unit time. They are independent: a compressor can deliver high pressure at low flow (a nailer) or low pressure at high flow (a paint sprayer). Pressure only enters airflow as a reference condition, which is exactly why the SCFM↔ACFM conversion needs a pressure input. So pick your tool by what you actually need: pressure rating, or flow rating.
For hp to CFM, piston compressors deliver very roughly 3.5–4 CFM per hp at ~90 psi and rotary screws nearer 4–5; the tab states its assumption so you can adjust it. It is a ballpark, not a nameplate.
Airflow conversion reference table
| CFM | m³/h | m³/s | L/s | Tons |
|---|
Airflow conversion FAQ
How do I convert CFM to m³/h?
Multiply CFM by 1.699 to get cubic metres per hour (m³/h, also written CMH). One cubic foot is 0.0283168 m³ and there are 60 minutes in an hour, so 1 CFM = 0.0283168 × 60 = 1.699 m³/h. To go back, divide m³/h by 1.699. For example 400 CFM is about 680 m³/h, and 1000 m³/h is about 589 CFM.
What is the difference between SCFM and ACFM?
SCFM is the flow at standard reference conditions (commonly 14.7 psia, 60 °F, 0% humidity) — the number on the label. ACFM is the actual volumetric flow at your real pressure and temperature — the number in the field. They are equal only at standard conditions. The converter applies ACFM = SCFM × (P_std / P_act) × (T_act / T_std) with absolute pressure and absolute temperature, so you can see how altitude, pressure and heat change the real flow.
Can you convert psi to CFM?
No — psi and CFM measure different things and are not directly convertible. PSI is pressure (force per area); CFM is volumetric flow (volume per time). A compressor can deliver high pressure with low flow or low pressure with high flow. Pressure only enters airflow as a reference condition, which is why SCFM↔ACFM needs a pressure input.
How many CFM per ton of air conditioning?
The rule of thumb is about 400 CFM per ton of cooling, with a typical range of 350–450 CFM/ton (drier climates lean lower, humid climates higher). So a 2-ton system moves roughly 800 CFM and a 3-ton about 1200 CFM. Remember a ton of cooling is 12,000 BTU/h of capacity, which is not the same thing as airflow.
How do I convert CFM to fpm?
CFM and fpm (feet per minute) are not interchangeable on their own — you need the duct area. Velocity (fpm) = CFM ÷ area (ft²), and CFM = fpm × area. Enter any two of CFM, velocity and area and the converter solves the third. To size a duct from a target velocity or friction, use the duct size calculator.
How much CFM does an air compressor produce per hp?
A rough rule for piston compressors is about 3.5–4 CFM per hp at around 90 psi; rotary-screw units are often nearer 4–5 CFM/hp. These are approximations that depend on pressure, efficiency and duty, so the hp↔CFM tab states its assumption (≈4 CFM/hp at ~90 psi) and should be treated as a ballpark, not a spec.