Pressure Drop Calculator

Estimate friction and fitting-related pressure drop for a pipe run using Darcy–Weisbach. Enter the actual fluid properties and internal pipe geometry for your operating condition.

Fittings worksheet

Enter the quantity and K value for each fitting from your project data or manufacturer documentation.

No fittings added. Use the additional K field above if you already have one combined value.

Fittings subtotal: 0 K

Total pressure drop0.21559 bar3.1269 psi · 21,559.3 Pa
Total head loss2.2024 mMajor 2.2024 m · minor 0 m
Major-loss share100%21,559.3 Pa from straight-pipe friction
Minor-loss share0%0 Pa from fittings and added K
Velocity / Reynolds number1.0186 m/sRe 50,736 · Turbulent
Friction factor0.02082Swamee–Jain explicit approximation · ε/D 0.00003

Scope: Darcy–Weisbach is used for steady, single-phase internal flow. Transitional-flow results are uncertain. This is not for compressible-gas networks, two-phase flow, slurry, pump selection or final code-compliant design.

Method and variables

Major loss: hf = f(L/D)(v²/2g). Minor loss: hm = K(v²/2g). Pressure drop: ΔP = ρg(hf + hm).

The tool uses f = 64/Re in laminar flow and the explicit Swamee–Jain approximation for non-laminar flow. It displays the Reynolds number so the result can be judged in context.

Worked example

For water near 20 °C flowing at 2 L/s through 100 m of 50 mm commercial-steel pipe, enter the fluid density, viscosity and roughness with K = 0 for straight-pipe loss. Add each valve, bend and other fitting in the worksheet with its project-specific quantity and K value, or enter one combined K value when that is all you have.

Important limits

Results in the transitional range are inherently uncertain. Roughness presets are editable references, not material certification. The calculation does not include elevation change, pump curves, non-circular geometry, transient effects, gas compressibility, two-phase flow, slurry, corrosion allowance or a design standard.

References

Related tools

Pipe Flow Rate & Velocity Calculator · Reynolds Number Calculator · Fluids & Piping Calculators

Frequently asked questions

What equation does this pressure-drop calculator use?
It uses Darcy–Weisbach: h_f = f(L/D)(v²/2g), plus a user-entered minor-loss term K(v²/2g). Pressure drop is then ΔP = ρgh. Results break out the straight-pipe and fitting-related portions.

How do I add fittings to the pressure-drop calculation?
Use the fittings worksheet to add a description, quantity and K value for each fitting. The calculator totals those K values and combines them with any additional combined K value you enter.

Why do density and viscosity matter?
They set the Reynolds number and translate head loss into pressure. Their values can change substantially with fluid type and temperature.

Can I use this for gas piping?
No. The calculator assumes steady single-phase internal flow without compressibility effects. Use a method intended for the gas, pressure range and governing standard.