Volumetric Flow Converter
L/s, L/min, m³/h, US GPM, and CFM — pump curves to duct specs.
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The engineering
Each trade owns a unit: US pump curves and plumbing run GPM, HVAC air-side runs CFM, European process datasheets run m³/h, and lab instruments run L/min or L/s. The same centrifugal pump exported both directions carries two nameplates — 100 GPM is 22.71 m³/h, and misreading which one the curve uses puts you 4× off.
The classic mistakes: assuming a gallon is a gallon (the imperial gallon is 4.546 L, 20% bigger than the US 3.785 L — a UK-spec pump datasheet will burn you), and quietly mixing standard and actual volumetric flow for gases (SCFM vs ACFM differ by the whole pressure ratio; this card converts volumes, not gas states).
Where this math comes from
The gallon fork is old politics: the US gallon descends from the 1707 Queen Anne wine gallon of 231 cubic inches, while Britain replaced its zoo of gallons with a new imperial gallon in the Weights and Measures Act of 1824 — after independence, so America never adopted it. Every GPM mismatch since is that split echoing.
Measuring flow (rather than just collecting it in a bucket) came from hydraulics: Giovanni Battista Venturi described the constricted-tube pressure drop in 1797, and Clemens Herschel turned it into the commercial venturi meter in 1887 to bill Holyoke's mills for canal water — flow as a number you could sell. HVAC's CFM and the metric m³/h grew up separately on either side of the Atlantic, and plant engineers have been converting at the interface ever since.
- 1707Queen Anne statute231 in³ wine gallon — ancestor of the US gallon.
- 1797Giovanni Battista VenturiConstricted-tube effect behind flow metering.
- 1824UK ParliamentImperial gallon defined — the US/imperial fork is permanent.
- 1887Clemens HerschelCommercial venturi meter — flow becomes a billable number.
See the full timeline of the math behind every calculator →
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