Fitting Loss Calculator
Enter flow, the true pipe inside diameter, a Darcy friction factor, and either a total loss coefficient or individual K values with quantities. Fluid density is optional and is used only for pressure drop.
A QUICK WALKTHROUGH
How to use this tool
- Enter flow in L/s, inside diameter in mm, and Darcy friction factor f.
- Enter total K directly; optionally add component K values and quantities to include their sum.
- Optionally enter density in kg/m³ to calculate pressure drop.
Equations and sources
For a full circular pipe, A = πd²/4 and v = Q/A. Velocity head is v²/(2g); fitting head loss is h = ΣK·v²/(2g). Pressure drop is Δp = ρgh. Equating this to Darcy–Weisbach straight-pipe loss gives Lₑ = ΣK·d/f, using the Darcy friction factor. References: New Mexico Water Resources Research Institute, Steady Flow Analysis of Pipe Networks, §3 and Eq. 4-8 (https://nmwrri.nmsu.edu/footer_pages/nm-wrri-library-database-files/wrri-library-pdfs/wrrilibrary7/007529.pdf); U.S. EPA, EPANET 2.2 User Manual, pipe headloss and minor-loss coefficient (https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10113EM.TXT).
Inputs and units
Flow is entered in L/s, diameter in mm, density in kg/m³, and f and K are dimensionless. The optional component rows add K × quantity to the directly entered base K. Supply coefficients from an appropriate source for the actual fitting, geometry, flow regime, and reference velocity; this calculator provides no fitting K table or defaults.
Scope
This is a steady, single-phase, incompressible-flow estimate for a full circular pipe using one representative mean velocity and one supplied Darcy friction factor. It calculates fitting loss only. It does not calculate straight-pipe distributed/friction loss, elevation or pump effects, changing pipe areas, or select/validate K or f. Results are not a design or safety approval.
GOOD TO KNOW
Common questions
Does this include straight-pipe friction loss?
No. It estimates fitting minor loss and the equivalent straight length for that fitting loss. It does not add actual pipe length or calculate distributed loss.
Where do K and f come from?
Enter values selected for the actual system from a trusted engineering reference, manufacturer, or applicable standard. K depends on fitting geometry and conditions; the calculator supplies no lookup table.
Do I need density?
No. Velocity, velocity head, fitting head loss, and equivalent length do not use density. Enter density in kg/m³ only when you want pressure drop in pascals.