Pressure Drop through Fittings Calculator
Estimate the pressure drop caused by pipe fittings — elbows, tees, valves and bends — using the velocity-head (K) method. Add up the loss coefficient K of every fitting on the run, enter the flow velocity, and get the head loss in metres and the pressure loss in kPa.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Look up the loss coefficient K for each fitting on the pipe run (e.g. elbow ≈ 0.9, gate valve ≈ 0.2, branch tee ≈ 1.8) and add them together to get the total K value.
- Enter the flow velocity in the pipe in metres per second — use the pipe-velocity calculator first if you only know the flow rate and bore.
- Leave density at 1000 kg/m³ for water, or change it for another fluid, and read off the head loss and pressure loss.
How it works
Fittings create local (minor) losses that scale with the velocity head: hL = K · v²/(2g), where K is the summed loss coefficient of all fittings, v is the flow velocity, and g = 9.81 m/s². The pressure loss is then hL · ρ · g ÷ 1000 in kilopascals. This is the classic K-method for fitting losses, separate from the Darcy friction loss along the straight pipe.
Worked example
Worked example. A run has three 90° elbows (0.9 each) and one gate valve (0.2), giving a total K of about 2.9. At a velocity of 1.5 m/s in water, the velocity head is 0.1147 m, so the head loss is 2.9 × 0.1147 ≈ 0.333 m, which is about 3.26 kPa of pressure drop across those fittings.
Common mistakes
- Forgetting to add up every fitting — the total K is the SUM of all the individual coefficients on the run, not just one.
- Using the wrong velocity: K-losses use the velocity in the pipe the fittings sit in, so recompute v if the bore changes.
- Mixing this up with straight-pipe friction loss — the two are added together to get the total drop, they are not alternatives.
Frequently asked questions
Where do I get the K values?
From fitting manufacturers' data or standard hydraulics tables. Common approximations are 0.9 for a 90° elbow, 0.2 for an open gate valve, 1.8–2.0 for a tee through the branch, ~10 for an open globe valve, 0.5 for a sharp pipe entry and 1.0 for an exit.
How does this relate to the equivalent-length method?
Both estimate the same fitting losses. The K (velocity-head) method used here multiplies K by v²/(2g); the equivalent-length method instead adds a fictitious length of straight pipe to the Darcy friction calculation. They should give broadly similar results.
Related tools
- Pipe Velocity Calculator
- Pipe Flow Calculator
- Friction Loss Calculator
- Darcy-Weisbach Head Loss Calculator
- Water Hammer Pressure Calculator
- Nozzle Flow Calculator
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Tip: Enter any known values to calculate the remaining results.
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