Differential Pressure Calculator
Compare upstream and downstream pressure across a component or fluid system. This general pressure differential calculator is separate from the pipe-friction model used by the pipe pressure-drop calculator.
Advanced: gauge/absolute reference and fluid head
Gauge pressures are measured relative to local atmosphere; absolute pressures are measured relative to a vacuum. Use the same reference system for both inputs. Negative gauge pressure is valid, but an absolute pressure should not be negative.
How the differential pressure formula works
The signed differential is ΔP = Pupstream − Pdownstream. A positive result means upstream is higher; a negative result means downstream is higher. Fluid head uses h = ΔP / (ρ × g), with density ρ and gravity g = 9.80665 m/s².
Worked example
For 120 kPa upstream and 100 kPa downstream, the differential is 20 kPa, or about 2.90 psi. With 998 kg/m³ water, that is about 2.04 m of fluid head.
Assumptions and limitations
- Both readings must use the same gauge or absolute reference.
- The tool compares measured pressures; it does not calculate Darcy-Weisbach friction loss.
- Head is an equivalent static fluid column, not a prediction of pump performance.