GPM to LPM calculator

U.S. fire-flow and sprinkler sheets usually list flow in gallons per minute (gpm), while metric notes and many international product sheets use liters per minute (L/min or lpm). Using the U.S. liquid gallon, 1 gpm = 3.785412 L/min (exactly 3.785411784 L per U.S. gal), so gpm × 3.785412 = L/min and L/min ÷ 3.785412 = gpm. This page is a free browser converter either direction. It is for learning and quick checks—not a substitute for the criteria adopted by your authority having jurisdiction, manufacturer data, a sealed hydraulic calculation, or review by a licensed design professional. It is not a design stamp and not a PE seal.

How the conversion is used

1. Confirm which unit your source report or datasheet uses (gpm on most U.S. fire-flow sheets; L/min on many metric / international sheets).
2. Convert with the U.S. liquid gallon factor: Q_L/min = Q_gpm × 3.785412, or Q_gpm = Q_L/min / 3.785412.
3. Keep the same flow meaning (rated pump flow, test flow, or demand) when you switch units—do not mix residual pressure from one test with a converted flow from another without checking the report.
4. After units match, continue with friction loss, hydrant, tank duration, or pump sketches in consistent units.

Free calculator

Educational approximation only. Uses 1 gpm = 3.785412 L/min (U.S. liquid gallons). Nothing you enter leaves your browser. For CFS conversions see GPM to CFS and CFS to GPM. For tank run-time see the water supply duration calculator. Multi-segment paths live in the Sprinkler Pipe Friction Loss workbook.

Worked example

A datasheet lists 250 gpm: 250 × 3.785412 ≈ 946.4 L/min. Conversely, 1,000 L/min ÷ 3.785412 ≈ 264.2 gpm. Always confirm whether the source used U.S. liquid gallons (this page) versus another gallon definition, and check the result against the adopted edition, manufacturer data, and AHJ—not this page alone.

Next steps: convert to CFS with the free GPM to CFS calculator, sketch supply with the hydrant flow test calculator, estimate tank run-time with the water supply duration calculator, size segment losses with the friction loss calculator or Hazen-Williams friction loss calculator, and build multi-segment paths in the Sprinkler Pipe Friction Loss workbook ($29). Pump and tank tables live in the Fire Pump & Tank Sizing workbook ($49).