Differential Pressure Calculator — ΔP with Unit Conversions
Calculate the pressure difference between two points in any pressure unit — Pa, kPa, bar, psi, mmHg, inH₂O and more — then optionally estimate the resulting flow velocity from Bernoulli's equation for incompressible fluids.
Pressure unit
kg/m³
Positive = P1 > P2 (normal flow direction); negative = reverse differential
- 1
P1 in Pa
200 kPa × 1,000 = 200,0001 kPa = 1,000 Pa - 2
P2 in Pa
150 kPa × 1,000 = 150,000 - 3
ΔP = P1 − P2
200,000 − 150,000 = 50,000
How does this calculator work?
Differential pressure ΔP = P1 − P2. Enter both pressures and choose a unit; the tool converts ΔP to Pa, kPa, bar, psi, mmHg and inH₂O instantly. With fluid density entered, it also estimates flow velocity v = √(2|ΔP|/ρ) from Bernoulli's equation (ideal, same-elevation, incompressible flow).
Formula
How this is calculated
Differential pressure (ΔP) is the signed difference between pressure at two points in a system: ΔP = P1 − P2. It is fundamental in fluid systems for measuring flow through orifices and nozzles, quantifying pressure drop across filters, valves and heat exchangers, and detecting blocked lines or failing pumps. The sign tells you the direction of the pressure gradient: positive ΔP means P1 is higher than P2, driving flow from upstream to downstream; negative ΔP indicates a reverse gradient.
Bernoulli's equation for steady, incompressible, frictionless flow between two points at the same elevation relates pressure and velocity: P1 + ½ρv1² = P2 + ½ρv2². If one side is a large reservoir (v1 ≈ 0) the equation simplifies to v2 = √(2ΔP / ρ), where ρ is the fluid density. This is the form used to derive flow rate from a differential pressure measurement — the principle behind orifice plates, Venturi meters and Pitot tubes. Real systems add discharge coefficients and correction factors for viscous losses, but the Bernoulli result is the starting point.
This calculator converts ΔP to eleven common pressure units so you can compare readings from different instruments without manual conversion. The velocity estimate is the ideal Bernoulli figure; for flow-metering applications, multiply by the appropriate discharge coefficient (typically 0.6–0.98 depending on geometry).
Frequently asked questions
Absolute pressure is measured relative to a perfect vacuum. Gauge pressure is absolute pressure minus local atmospheric pressure. Differential pressure is simply the difference between two pressures — neither needs to be atmospheric. ΔP sensors measure the difference directly and are often used where neither side is at atmosphere.
Use the density of the flowing fluid at operating conditions: water at 20°C ≈ 998 kg/m³, seawater ≈ 1025 kg/m³, air at 20°C and 1 atm ≈ 1.204 kg/m³, natural gas varies but is often 0.7–0.9 kg/m³ at line conditions. For gases, density changes significantly with pressure and temperature — use the ideal-gas law or a properties table for accuracy.
Bernoulli's equation includes a hydrostatic (elevation) term: P + ½ρv² + ρgh = constant. When the two measurement points are at different heights, the ρg·Δh term contributes to the pressure difference independently of flow velocity. This calculator omits the elevation term; for significant height differences, add ρ × g × Δh (in Pa) to the measured ΔP before calculating velocity.
Also known as
TG we-Calculate Editorial Team. (2026). Differential Pressure Calculator — ΔP with Unit Conversions [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/differential-pressure-calculator
TG we-Calculate Editorial Team. "Differential Pressure Calculator — ΔP with Unit Conversions." TG we-Calculate. 2026. https://we-calculate.com/calculator/differential-pressure-calculator.
TG we-Calculate Editorial Team, "Differential Pressure Calculator — ΔP with Unit Conversions," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/differential-pressure-calculator
@misc{wecalculate_differential_pressure_calculator, title = {Differential Pressure Calculator — ΔP with Unit Conversions}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/differential-pressure-calculator}}, year = {2026}, note = {TG we-Calculate} }
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