Pumping Formulas

Malcolm Thompson Pumps provides a range of pump tools including Pumping Formulas, Conversion Tables and a Glossary of Terms which can be used to assist with pump selection. To best ensure your pump choice meets your requirements, please contact one of our experienced customer service team members on 1800 439 607 who can assist with pump selection, specifications and a competitive quote.

Pumping Formula for any liquid

Volumic flow from mass flow & density
For any liquid
Vol flow (l/s) = 1000 * Mass Flow (kg/s)

Density (kg/m3)

Head of liquid from pressure & density
For any liquid
Head (m) = 102.0 * Pressure (kPa)

Density (kg/m3)

Pump input power from pump performance
For any liquid
Power (kW) = Density (kg/m3) * Volumetric Flow (l/s) * Head (m)

1000 * 102.0 * Efficiency (decimal)

Pump input power from kilowatt – hour meter
Power (kW) = 36 * Disc.Revs. * Meter Ratio Constant * Motor Efficiency (dec)

Time (s) * Meter Disc. Constant (rev/kW-h)

Pump input power from current and voltage
Power (kW) = Current (A) * Voltage (V) * Motor Efficiency (dec) * Pump Efficiency (dec)

57 735

Motor input energy per volume of liquid pumped
For any liquid
Energy/ Volume (kW-h/kl) = Density (kg/m3) * Head (m)

367 347 * Motor Efficiency (dec) * Pump Efficiency (dec)

Pump input power from engine
Power (kW) = Pi * Torque (N.m) * Speed (rpm)

30 000

= Torque (N.m) * speed (rpm)

9 549

Pumping Formula for water at 20 degrees C

Volumetric flow from mass flow
Vol flow (l/s) = 1.002 * Mass Flow (kg/s)
Head of liquid from pressure
Head (m) = 0.1022 * Pressue (kPa)
Head (ft) = 0.3354 * Pressure (kPa)
Pump input power from pump performance
Power (kW) = volumetric flow (l/s) * Head (m)

102.2 * Efficiency (decimal)

Motor input energy per volume of liquid pumped
energy/volume (kW-h/kl) = Head (m)

368.0 * Motor efficiency (dec) * pump efficiency (dec)

Average velocity of flow
Through a circular section
Velocity of flow (m/s) = 1273 * Volumetric Flow (l/s)

[Diameter (mm) ] squared

Through any area normal to the direction of flow
Velocity of Flow (m.s) = 1000 * Volumetric Flow (l/s)

Area (mm2)