Pressure Drop Calculator
How much pressure — and pump head — you lose pushing a fluid through a pipe. Darcy-Weisbach with automatic friction factor, so you size the pump for the real loss, not a guess.
Why Pressure Drop Decides Your Pump
Every foot of pipe, every fitting and every gallon per minute costs you pressure. Undersize the pipe and the pump has to fight a huge loss; oversize it and you have spent money on copper you did not need. Pressure drop is the number that sets that balance, and it is what tells you the head your pump actually has to deliver.
The Darcy-Weisbach Equation
The friction factor f depends on the flow regime. Below a Reynolds number of about 2300 the flow is laminar and f = 64/Re. Above it the flow is turbulent and f comes from the pipe roughness and Reynolds number — this calculator uses the Swamee-Jain equation, an explicit form of the Colebrook relation, so you do not have to iterate.
Keep an Eye on Velocity
For most liquid systems a velocity of roughly 2 to 8 ft/s (0.6 to 2.4 m/s) is the comfort zone. Below about 2 ft/s solids can settle out; above 8 to 10 ft/s you invite noise, water hammer and erosion. The calculator flags where your design lands.
Frequently Asked Questions
Does this include fittings and valves?
No — it covers straight pipe. Elbows, tees and valves add loss, usually handled as equivalent length or K-factors. On short runs with many fittings, those can outweigh the pipe itself.
What is head loss versus pressure drop?
They are the same loss expressed two ways. Head loss is in feet or metres of fluid; pressure drop is in psi, kPa or bar. Pump curves are usually plotted in head, so both are reported.
Can I use it for non-water fluids?
Yes — set the specific gravity and viscosity, or pick a fluid preset. Viscosity has a big effect in the laminar range.
Related calculators
- Pipe Flow Calculator — flow rate, velocity and sizing in one place.
- Reynolds Number Calculator — find the flow regime behind the friction factor.
- Pump Horsepower Calculator — turn this head into pump power.
- Engineering Unit Converter — psi, kPa, bar and more.