Pressure & Flow Unit Converter

These free online calculators allow you to convert between the pressure and flow rate units most commonly encountered in fire protection and hydraulic engineering. Whether you are working to BS EN 12845, BS 9251, NFPA 13, or another international standard, the converters below support instant conversion without the need for manual calculation.

Enter a value in any of the four fields and the remaining units will update automatically. You can type directly into whichever unit you are working in — there is no need to select a "from" or "to" unit first.

The four units covered are:

• bar — the most common unit in European fire sprinkler system design, used throughout BS EN 12845 and BS 9251.

• m H₂O (metres head) — expresses pressure as an equivalent height of water. Frequently used in hydraulic calculations and pump specifications.

• psi (pounds per square inch) — the standard unit in US-based standards such as NFPA 13, and widely used in imported equipment datasheets.

• kPa (kilopascals) — the SI unit for pressure, sometimes seen in Australian and other international standards.

The reference table shows the fixed equivalent of 1 bar across all four units, useful as a quick sanity check.

Enter a value in any of the four fields and the remaining units will update automatically. You can type directly into whichever unit you are working in — there is no need to select a "from" or "to" unit first.

The four units covered are:

• L/min (litres per minute) — the standard flow rate unit in European fire sprinkler standards, including BS EN 12845 and BS 9251, and the primary unit used throughout FHC.

• L/s (litres per second) — commonly used in civil and water supply engineering, and sometimes seen in pump performance data.

• m³/h (cubic metres per hour) — widely used in HVAC, industrial, and water treatment applications, and often quoted on larger pump curves.

• US gal/min (US gallons per minute) — the standard unit in American fire protection standards such as NFPA 13, and commonly found on imported pumps and equipment manufactured to US specifications.

Pressure is a measure of force applied over a given area. In fire protection engineering, several units are commonly used depending on the standard, region, or equipment involved, which is why conversion between them is a routine part of hydraulic design work.

The SI unit of pressure
The internationally recognised SI unit of pressure is the pascal (Pa), defined as one newton per square metre (N/m²). Because a pascal is a very small quantity, practical engineering work almost always uses the kilopascal (kPa, equal to 1,000 Pa) or, in some contexts, the megapascal (MPa, equal to 1,000,000 Pa).

Bar
The bar is not an SI unit, but it is accepted for use alongside the SI system and remains the dominant unit in European fire sprinkler standards, including BS EN 12845 and BS 9251. One bar is approximately equal to atmospheric pressure at sea level, and is defined as exactly 100,000 Pa (100 kPa).

Metres head (m H₂O)
Metres head expresses pressure in terms of the equivalent height of a static column of water. It is widely used in pump engineering and hydraulic network calculations because it relates directly to the physical height difference between a water source and the point of discharge. One metre head is approximately 0.098 bar.

PSI (pounds per square inch)
PSI is an imperial unit that remains in standard use in the United States and is therefore the pressure unit throughout NFPA 13 and related American standards. It is also commonly found on imported pumps, pressure gauges, and equipment manufactured to US specifications. One psi is approximately 0.069 bar.

Flow rate describes the volume of fluid passing a given point per unit of time. In fire protection engineering, flow rate appears throughout hydraulic calculations — from the discharge requirements of individual sprinkler heads to the total demand placed on a water supply or pump set.

The SI unit of flow rate
The SI unit of volumetric flow rate is the cubic metre per second (m³/s). In practice this is far too large for most fire protection work, so the litre per minute (L/min) and litre per second (L/s) are the units most commonly encountered in European standards and calculation software. One litre per second equals 60 litres per minute.

Litres per minute (L/min)
Litres per minute is the dominant unit in UK and European sprinkler design, used throughout BS EN 12845 and BS 9251 for both individual head flows and system demand figures. It is the native unit in FHC.

Litres per second (L/s)
Litres per second is frequently used by water utilities and civil engineers when specifying available flow at a supply point, and is common in pump engineering. Converting between L/s and L/min is straightforward — multiply by 60 or divide by 60.

Cubic metres per hour (m³/h)
Cubic metres per hour is the preferred flow unit in much of continental European industry and is routinely seen on pump performance curves, particularly for larger commercial pumps. One m³/h is equal to 1,000 litres per hour, or approximately 16.67 L/min.

US gallons per minute (US gal/min)
US gallons per minute is the standard unit in American fire protection, used throughout NFPA 13 and related standards for sprinkler discharge densities, pipe sizing tables, and water supply requirements. Note that the US gallon (3.785 litres) differs from the UK imperial gallon (4.546 litres), so care is needed when working with mixed documentation.