单位重量液体通过泵所获得的能量叫扬程。泵的扬程包括吸程在内，近似为泵出口和入口压力差。又称为水头（hydraulic head）或落差。

扬程用H表示，单位为米（m）。泵的压力用P表示，单位为MPa（兆帕）

H=P/ρ

如P为1 kg/cm，ρ（水）为1000 kg/m

则H=(1 kg/cm)/(1000 kg/m)

H=(1 kg/cm)/(1000 kg/m)=(10000 kg/m)/(1000 kg/m)=10 m

1 MPa=10 kg/cm

得H=(P2-P1)/ρ =ΔP/ρ

（P2=出口压力P1=进口压力ΔP=压力差）

Hydraulic head or piezometric head is a specific measurement of liquid pressure above a geodetic datum.

It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer. In an aquifer, it can be calculated from the depth to water in a piezometric well (a specialized water well), and given information of the piezometer's elevation and screen depth. Hydraulic head can similarly be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common datum. The hydraulic head can be used to determine a hydraulic gradient between two or more points.