Plumbing Unit Converter — Flow, Pressure, Head & Volume
Pump curves come in feet, supply pressure in psi, European fixtures in bar and litres per minute, and civil drawings in cubic feet per second. This converts between all of them and shows the whole category at once — plus the factor it used, so you can check it.
Convert
Result
10 US gallons per minute (gpm) = 37.8541 Litres per minute (L/min)
The factor used
× 3.785412
And back the other way
1 Litres per minute (L/min) = 0.264172 US gallons per minute (gpm)
Everything in this category
Metric factors are exact by definition. The pressure-to-head conversion depends on water density and is quoted at 60 °F, so it shifts slightly with temperature.
The conversions, explained in plain English
Everything here is one multiplication, except the one that is not.
Which gallon?
An imperial gallon is 1.201 US gallons — a 20% difference. On a fixture flow rate that is easily a whole pipe size, and spec sheets rarely say which one they mean.
Rises are not temperatures
Converting a 90 °F temperature rise gives 50 °C, not 32.2 °C. Only the ratio applies to a difference; the offset belongs to an absolute reading. This is the most common conversion mistake in water heating.
Feet of head is physical
Pump curves use feet because feet are independent of fluid density — the same curve works for any liquid. Converting to psi puts water's density back in, which is why that factor is not a definition.
Bar catches people out
A European fixture wanting "3 bar" wants 43.5 psi at the inlet — several times what a typical US fixture needs, and enough to change how you size the supply.
Worked examples
A European pump curve, an imported fixture spec, and the temperature-rise trap.
A pump curve in metric
A datasheet quotes 2.3 m³/h at 18 m of head.
18 m of head = 59.1 ft = 25.6 psi
Result: about 10 gpm at 59 feet — now comparable against a US pump curve and against a total dynamic head figure.
The imperial gallon trap
A UK spec sheet lists a fixture at 3 gallons per minute. Which gallon?
actually imperial: 3 × 1.20095 = 3.60 US gpm
→ 20% under-counted if you assume US
Result: a 20% error on every fixture in the schedule. Across a building that is enough to undersize the main — and the spec sheet almost never spells out which gallon it means.
Converting a temperature rise
A water heater needs a 90 °F rise. What is that in Celsius?
right: 90 × 5/9 = 50.0 °C
because a difference has no zero point to offset
Result: 50 °C. Use the converter's temperature mode for an actual thermostat setting, and the ratio alone for a rise — getting this wrong understates the heating load by more than a third.
10 gpm in every flow unit
Computed from the same code the converter runs.
| Unit | 10 gpm equals |
|---|---|
| Litres per minute (L/min) | 37.8541 |
| Litres per second (L/s) | 0.6309 |
| Cubic metres per hour (m³/h) | 2.2712 |
| US gallons per hour (gph) | 600.0000 |
| Cubic feet per second (cfs) | 0.0223 |
| Imperial gallons per minute | 8.3267 |
60 psi in every pressure unit
| Unit | 60 psi equals |
|---|---|
| Feet of water column (ft) | 138.536 |
| Bar | 4.137 |
| Kilopascals (kPa) | 413.685 |
| Metres of water column (m) | 42.226 |
| Atmospheres (atm) | 4.083 |
The anchors worth knowing
The handful that come up daily, and which of them are exact.
| This | Equals | Note |
|---|---|---|
| 1 US gallon | 3.785412 litres | exact by definition |
| 1 imperial gallon | 1.20095 US gallons | a 20% trap on spec sheets |
| 1 inch | 25.4 mm | exact by definition |
| 1 psi | 2.309 ft of head | water at 60 °F, not a definition |
| 1 bar | 14.5038 psi | European pump and fixture data |
| 1 cfs | 448.83 gpm | 7.48052 gal/ft³ × 60 s |
| 1 m/s | 3.28084 ft/s | exact by definition |
| 0 °C | 32 °F | offset scale — needs the +32 |
Sources & standards: metric conversions are exact by international definition — the inch is 25.4 mm and the US gallon is 3.785411784 litres. The psi-to-head factor is derived from the density of water at 60 °F, the same constant used across these plumbing calculators, and is not a definition. Every conversion on this page is verified to round-trip exactly.
Frequently asked questions
Common questions about plumbing unit conversions and the traps in them.
How many litres per minute is 10 gpm?
37.8541 L/min. One US gallon is exactly 3.785411784 litres by definition, so the factor is exact rather than rounded. Going the other way, 100 L/min is 26.42 gpm.
How do I convert psi to feet of head?
Multiply psi by 2.309, or feet by 0.4331. So 60 psi is 138.5 feet of water column. Unlike the metric conversions this one is not a definition — it comes from the density of water at 60 °F, so it shifts very slightly with temperature.
Why is an imperial gallon different from a US gallon?
They are separate historical definitions that were never reconciled. An imperial gallon is 4.54609 litres against the US gallon's 3.785411784 — about 1.201 US gallons. On a fixture flow rate that is a 20% error, which is more than enough to change a pipe size. Always check which gallon a spec sheet means.
What is a bar in psi?
14.5038 psi. Bar is common on European fixture and pump data, so 3 bar of required inlet pressure is 43.5 psi — well above the 8 to 15 psi most US fixtures want, and worth catching before you size the supply.
Why is temperature handled differently?
Because the scales have different zero points, not just different sizes of degree. Every other conversion here is a single multiplication; temperature needs an offset as well, so °F = °C × 9/5 + 32. That is also why a temperature rise converts differently from a temperature: a 90 °F rise is a 50 °C rise, not 32.2 °C.
Is 1 cfs really 448.83 gpm?
Yes — 448.83 gpm, which is just 7.48052 gallons per cubic foot times 60 seconds. Cubic feet per second turns up in storm drainage and municipal work rather than building plumbing, but it is the unit a civil engineer will hand you.
Are these factors exact?
The metric ones are, by definition: the inch is exactly 25.4 mm and the US gallon is exactly 3.785411784 litres. The water-based ones — psi to feet of head — depend on water density and are quoted at 60 °F. Every conversion on this page round-trips exactly, which is verified by test rather than assumed.
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