How this calculator works
The Darcy-Weisbach equation balances wall friction against pressure loss in a full, straight pipe. Supply a Darcy friction factor for the operating Reynolds number and roughness. Inverse diameter and velocity modes hold that factor fixed, so a design change may require recalculating it. Fittings, elevation changes and pump head are excluded.
Formula
Delta p = f (L/D) rho v^2/2. The Darcy factor is four times the Fanning factor.
Worked example
A 10 m pipe with D = 0.1 m, rho = 1000 kg/m3, v = 2 m/s and f = 0.02 loses 4000 Pa. At 1 m/s the loss is 1000 Pa.
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Frequently asked questions
Is this total system pressure loss?
It is distributed pipe friction only. Add fitting losses and static elevation effects separately.
Which friction factor is required?
Use the Darcy factor. Multiply a Fanning factor by four before entering it.
Does the diameter solver update roughness effects?
No. It solves algebraically at the supplied factor; iterate with the friction-factor calculator if needed.