How to use this calculator
- Enter flow and hose ID. Use actual flow rate and actual inside diameter, not only the nominal dash size.
- Enter hose length. Use the full hose length, including bends routed through the machine.
- Set oil properties. Enter viscosity at operating temperature and specific gravity for the fluid.
- Add fitting losses. Enter the summed K value for fittings and couplers, then read Δp, velocity, Reynolds number and power loss.
How it works
Hose pressure drop is a pipe-flow loss:
Δp = (f·L/D + ΣK) · ρv²/2
where f is the Darcy friction factor, L/D is the hose
length-to-bore ratio, ΣK is the fitting loss coefficient, and
ρv²/2 is dynamic pressure. The calculator finds velocity from flow and
hose ID, then uses Reynolds number to choose laminar or turbulent friction.
Worked example
Verified against the live calculator
A 40 L/min pressure line through a 19 mm ID, 5 m hose with 46 cSt oil gives about 0.047 MPa pressure drop. Oil velocity is about 2.35 m/s, so the default case is in a reasonable pressure-line velocity range.
Frequently asked questions
How do you calculate hydraulic hose pressure drop?
Use Darcy-Weisbach: Δp = (f·L/D + ΣK)·ρv²/2. Flow and hose ID set velocity, viscosity sets Reynolds number and friction factor, and fittings add minor losses through the ΣK term.
Why does cold hydraulic oil drop more pressure?
Cold oil has much higher viscosity. Higher viscosity lowers Reynolds number and raises friction losses, so the same hose can drop far more pressure during cold startup than at operating temperature.
What is a good hydraulic hose velocity?
For pressure lines, roughly 3–5 m/s is a common starting range. Higher velocity increases pressure drop, heat and noise. Suction and return lines usually need lower velocities.
Should I include fittings?
Yes. Elbows, adapters, quick couplers and valves can dominate short hose runs. Add their minor-loss K values in the fitting coefficient field, or use vendor pressure-drop curves when available.
Method & assumptions
- Uses Darcy-Weisbach with laminar
f = 64/Reand the Swamee-Jain turbulent friction approximation. - Assumes steady, single-phase oil flow through a constant-ID hose.
- Oil viscosity must be entered at the actual operating temperature.
- Fitting loss coefficients are estimates; use manufacturer curves for quick couplers, valves and compact manifolds.