From this site

One project, every trade

Each calculator adds its lines to a single estimate — consolidated BOM, schedule and cash-flow included.

Open My Project →

GPM to Litres per Minute Calculator

Convert US gallons per minute into litres per minute for metric pump and fixture ratings.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Flow rate

10 gal/min

High confidence

1 US gallon = 3.785411784 L exactly, so GPM × 3.7854 gives L/min. A US gallon and an imperial gallon differ by about 20% — confirm which the source figure uses.

Conversion factor applied
1 gal/min per gpm

Pump curves, fixture ratings and design flows cross this boundary whenever equipment is sourced internationally. The conversion itself is exact, but the gallon is not a single unit: the US liquid gallon is 3.785 litres while the imperial gallon is 4.546, and a figure converted with the wrong one is twenty percent adrift — comfortably enough to undersize a pump or overstate a fixture's delivery. Note too that flow is only one input to pipe sizing. The same litres per minute through an undersized bore produces velocity noise, erosion over time and a pressure drop that starves outlets further along, so the converted figure needs to be checked against velocity limits rather than used alone.

Add the equipment this sizes

This result is a specification — 10 gal/min — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • 1 US liquid gallon = 231 cubic inches = 3.785411784 L exactly
  • 1 imperial gallon = 4.54609 L, roughly 20% larger than a US gallon

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

US gallons or imperial gallons?
This uses US gallons at 3.785 litres. An imperial gallon is 4.546 litres, about twenty percent larger, and older British data may use it. A flow figure converted with the wrong gallon is out by a fifth, which is more than most sizing margins tolerate.
Does flow rate alone size a pipe?
No. Pipe sizing balances flow against velocity and pressure loss. The same flow through too small a bore produces noise, erosion and excessive pressure drop, so the flow figure is an input to sizing rather than the answer.
How do fixture units relate to this?
They do not convert directly. Fixture units are a loading index that accounts for how likely outlets are to run simultaneously, and they are turned into a design flow through published tables rather than by arithmetic.