About Flow Rate Converter — CFM, GPM, L/s, m³/h & More
The flow rate converter translates volumetric flow between the units that air and water systems mix constantly: CFM from US fan and blower ratings, m³/h from European AHU datasheets and ErP declarations, L/s from ventilation codes, GPM from US pump curves, and L/min from plumbing fixtures. Every conversion runs through the SI base unit — the cubic meter per second — using NIST SP 811 Appendix B factors: 1 CFM = 4.719474×10⁻⁴ m³/s and 1 US gallon per minute = 6.309020×10⁻⁵ m³/s.
The anchors worth keeping in your head: 1 CFM ≈ 1.699 m³/h (so a 1,000 CFM fan is about 1,700 m³/h), 1 L/s = 3.6 m³/h exactly, and 1 GPM ≈ 0.0631 L/s. The GPM here is the US liquid gallon — an imperial GPM is about 20% larger — and flow is treated as a magnitude, so negative entries are rejected rather than silently converted.
How It Works
- Enter the flow value, pick its current unit ("from"), and pick the unit you need ("to"). The headline shows the converted value; the table beneath shows the same flow in all seven units at once.
- Every conversion is value × (m³/s per from-unit) ÷ (m³/s per to-unit). The metric ladder (m³/h, L/s, L/min) is exact by definition; CFM, GPM, and ft³/s carry the published NIST 7-significant-figure factors.
- Displayed values are rounded to 6 significant digits; the conversion itself runs in full double precision, so converting back returns your original number.
- Remember what a unit converter does not do: an air flow at duct conditions is a volume flow, and comparing it with a standard-condition rating (SCFM) needs a density correction, not a unit conversion. The same number of m³/h is a different mass flow at a different temperature.
Worked Example
A US-made ERV is rated 1,000 CFM and the European commissioning sheet wants m³/h. Through the base unit: 1,000 CFM × 4.719474×10⁻⁴ m³/s = 0.4719474 m³/s, and 0.4719474 × 3,600 = 1,699.01 m³/h — the chart's "1000 CFM" row. The same flow is 471.947 L/s; as a sanity check, a typical supply diffuser at 100 CFM is about 170 m³/h, and the table scales linearly.
CFM to m³/h conversion chart (with L/s and GPM)
Common fan and blower ratings converted with the NIST SP 811 factor 1 CFM = 4.719474×10⁻⁴ m³/s, shown to 6 significant digits — exactly what the converter outputs for the same inputs.
| Flow | m³/h | L/s | GPM |
|---|---|---|---|
| 100 CFM (bath fan, large) | 169.901 | 47.1947 | 748.052 |
| 250 CFM (range hood) | 424.753 | 117.987 | 1,870.13 |
| 400 CFM (1-ton airflow) | 679.604 | 188.779 | 2,992.21 |
| 1000 CFM (2.5-ton airflow) | 1,699.01 | 471.947 | 7,480.52 |
| 2000 CFM (5-ton airflow) | 3,398.02 | 943.895 | 14,961 |
Formulas
- Conversion through the base unit
x = value × f_from ÷ f_to- m³/s per unit (the factor table)
CFM 4.719474×10⁻⁴ · GPM 6.309020×10⁻⁵ · ft³/s 2.831685×10⁻² · m³/h 1/3,600 · L/s 10⁻³ · L/min 1/60,000- The everyday anchors
1 CFM ≈ 1.69901 m³/h; 1 L/s = 3.6 m³/h (exact); 1 GPM ≈ 0.0630902 L/s
Standards & References
- NIST SP 811, Guide for the Use of the International System of Units, Appendix B — conversion factors (ft³/min 4.719474×10⁻⁴ m³/s; US gal/min 6.309020×10⁻⁵ m³/s; ft³/s 2.831685×10⁻² m³/s)
- Exact definitions: 1 m³/h = 1/3,600 m³/s; 1 L/s = 10⁻³ m³/s; 1 L/min = 1/60,000 m³/s
- Volumetric basis: converting CFM at duct conditions to standard-condition ratings (SCFM) needs a density correction, which is outside unit conversion
Frequently Asked Questions
How do I convert CFM to m³/h?
Multiply CFM by 1.69901 (that is 4.719474×10⁻⁴ m³/s per CFM times 3,600 s/h). So 400 CFM ≈ 679.6 m³/h and 1,000 CFM ≈ 1,699 m³/h. Going the other way, multiply m³/h by 0.588578 to get CFM.
Which gallon does GPM use here?
The US liquid gallon: 1 US GPM = 6.309020×10⁻⁵ m³/s per NIST SP 811, about 3.785 L/min. The imperial (UK) gallon is 4.546 L — roughly 20% larger — so an imperial GPM figure converted with this tool would be off by that factor. US pump curves, fixture ratings, and irrigation equipment all quote US GPM.
Why does the converter reject negative flow values?
Because a bare flow number in a unit conversion context is a magnitude — "minus 500 CFM" on a fan schedule is a sign convention from some larger analysis, not a unit-conversion input. Rejecting negatives catches sign mistakes (a dropped minus from a pressure field, a stray hyphen) instead of silently converting them.
Is CFM the same as SCFM?
No. CFM here is actual volumetric flow at whatever conditions the air is at. SCFM re-expresses the flow at a defined standard density (commonly 0.075 lb/ft³), so it is really a mass-flow statement. Converting CFM to m³/h is pure unit arithmetic and this tool does it exactly; converting ACFM to SCFM requires the actual temperature and pressure, which is a density correction outside unit conversion.
How many CFM is a ton of cooling airflow?
The common rule of thumb is 350–400 CFM per ton of air conditioning, which is why the chart labels 400 CFM as 1-ton and 2,000 CFM as 5-ton airflow. That is a design heuristic, not a unit conversion — actual design airflow depends on the sensible heat ratio — but it makes the converted m³/h values easy to sanity-check against European equipment sized in kW.