Pipe pressure drop calculator (Darcy-Weisbach)

Darcy-Weisbach head loss and pressure drop for water in straight pipe, with fittings and a diameter comparison.

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	A	B	C
1	Pipe pressure drop calculator (Darcy-Weisbach)
2	Example data — replace the blue input cells with your own.
3
4	Flow and fluid
5	Fluid	Water	Water only; properties are on the Properties tab
6	Water temperature (°C)	20.0	0 to 100 °C; values between table rows are interpolated
7	Property table row used (helper)	5	Row of the Properties table used for interpolation
8	Density, ρ (kg/m³)	998.2
9	Dynamic viscosity, μ (Pa·s)	1.00E-03
10	Flow rate, Q (L/s)	1.50
11	Pipe internal diameter, D (mm)	52.5	Internal diameter, not nominal size. The Diameters tab compares sizes.
12	Pipe length, L (m)	120.0	Straight pipe only; add fittings in the table below
13	Pipe material	Commercial steel or wrought iron
14	Roughness from the Properties tab (mm)	0.045
15	Roughness override (mm, optional)		Leave blank to use the value from the Properties tab
16	Roughness used, ε (mm)	0.045

Showing the first 16 of 52 rows and 4 of 4 columns. Cells with formulas show the formula on hover.

	A	B	C	D
1	Water properties and pipe roughness
2	Example data — replace the blue input cells with your own. Property values are rounded from standard saturated-water tables.
3
4	Water properties (saturated liquid at 1 atm)
5	Temperature (°C)	Density, ρ (kg/m³)	Dynamic viscosity, μ (Pa·s)	Kinematic viscosity, ν (m²/s)
6	0	999.8	1.79E-03	1.79E-06
7	5	1,000.0	1.52E-03	1.52E-06
8	10	999.7	1.31E-03	1.31E-06
9	15	999.1	1.14E-03	1.14E-06
10	20	998.2	1.00E-03	1.00E-06
11	25	997.0	8.90E-04	8.93E-07
12	30	995.7	7.98E-04	8.01E-07
13	40	992.2	6.53E-04	6.58E-07
14	50	988.0	5.47E-04	5.54E-07
15	60	983.2	4.66E-04	4.74E-07
16	70	977.8	4.04E-04	4.13E-07

Showing the first 16 of 30 rows and 4 of 4 columns. Cells with formulas show the formula on hover.

	A	B	C	D	E	F	G	H	I	J	K	L
1	Pipe diameter comparison
2	Example data — replace the blue input cells with your own. Same flow, length, fittings and fluid as the Inputs tab; only the diameter changes.
3
4	Linked from the Inputs tab
5	Flow rate, Q (L/s)	1.50
6	Pipe length, L (m)	120.0
7	Density, ρ (kg/m³)	998.2
8	Dynamic viscosity, μ (Pa·s)	1.00E-03
9	Roughness, ε (mm)	0.045
10	Sum of minor loss coefficients, ΣK	8.00
11	Velocity limit (m/s)	3.0
12
13	Nominal size	Internal diameter (mm)	Velocity (m/s)	Reynolds number	ε/D	Friction factor, f	Friction head (m)	Minor head (m)	Total head (m)	Pressure drop (kPa)	Velocity check	Matches Inputs
14	DN15 (1/2 in)	15.8	7.650	120,419	0.002848	0.027	615.278	23.873	639.151	6256.65	Above the limit
15	DN20 (3/4 in)	20.9	4.372	91,034	0.002153	0.026	144.817	7.798	152.615	1493.95	Above the limit
16	DN25 (1 in)	26.6	2.699	71,527	0.001692	0.025	42.135	2.972	45.107	441.55	Within the limit

Showing the first 16 of 24 rows and 12 of 12 columns. Cells with formulas show the formula on hover.

	A
1	Pipe pressure drop calculator (Darcy-Weisbach)
2	Notes: what this workbook does, how to use it and the method behind it.
3
4	What it does
5	Calculates the friction and minor losses in a straight pipe carrying water: velocity, Reynolds number, friction factor, head loss in metres and pressure drop in kilopascals. A diameter tab compares standard sizes for the same flow.
6
7	How to use it
8	1. On the Inputs tab, enter the water temperature, flow rate, internal diameter and pipe length.
9	2. Choose the pipe material. Its roughness comes from the Properties tab; type an override only if you have a supplier value.
10	3. List the fittings and valves with their number in the fittings table. Use the K values or replace them with manufacturer data.
11	4. Read the velocity, Reynolds number, flow regime, friction factor, head loss and pressure drop.
12	5. Open the Diameters tab to see the same flow in each standard size, with velocity and pressure drop.
13
14	Formulas and method
15	Darcy-Weisbach: h_f = f × (L/D) × V²/(2g) and h_m = ΣK × V²/(2g). Total head h = h_f + h_m, in metres of water.
16	Pressure drop Δp = ρ × g × h, in pascals; the sheet shows kilopascals.

Showing the first 16 of 34 rows and 1 of 1 columns. Cells with formulas show the formula on hover.

What does this template do?

This calculator finds the head loss and pressure drop in a straight water pipe using the Darcy-Weisbach equation. Enter the water temperature, flow rate, internal diameter, pipe length and material. The sheet looks up the water density and viscosity, interpolates between table rows, and takes the pipe roughness from a material list.

Friction losses use the Darcy friction factor. Laminar flow below a Reynolds number of 2,300 uses f = 64/Re. Turbulent flow uses the Swamee-Jain explicit equation, which agrees with Colebrook to within 2% above a Reynolds number of about 12,000 and to within 3% from 5,000 upward. Minor losses come from a fittings table of K values, each multiplied by the number of fittings.

The results include the velocity, Reynolds number, flow regime, friction factor, head loss in metres and pressure drop in kilopascals. A Diameters tab repeats the calculation for nine standard steel sizes, so you can compare velocity and pressure drop at the same flow.

It suits preliminary pipe sizing and comparing options. Check results against the applicable standard and the manufacturer's data before specifying pumps or pipe.

What’s inside

Darcy-Weisbach head loss, with friction factor from 64/Re (laminar) or Swamee-Jain (turbulent)
Water density and viscosity interpolated from a 0 to 100 °C table with INDEX and MATCH
Roughness taken from a pipe material list, with an optional override
Minor losses from a fittings table: ΣK × V²/2g
Diameters tab compares nine Schedule 40 steel sizes at the same flow

Which tabs does the workbook have?

Tab	What it holds
Inputs	Water temperature, flow, diameter, length and material, the flow and friction results, the head loss, and the fittings table.
Properties	Water density and viscosity by temperature, and the pipe roughness values for each material.
Diameters	The same flow, length and fittings calculated for nine standard steel pipe sizes, with velocity and pressure drop.
Notes	What the workbook does, how to use it, the equations, the accuracy limits and the professional-verification note.

What formulas does this template use?

This template holds 143 formulas in 379 cells across 4 tabs, so 38% of its cells calculate. They use 8 distinct functions; the longest formula is 204 characters and 20 of them read from another tab.

Function	Uses	What it does
`IF`	43	one result when a test is true, another when false
`INDEX`	13	value at a position in a range
`LOG10`	10	base-10 logarithm
`PI`	10	the constant pi
`ABS`	9	absolute value
`MATCH`	2	position of a value in a range
`SUM`	2	adds numbers
`MIN`	1	smallest value

Counted from the workbook itself. Only functions that Excel, LibreOffice Calc, Google Sheets and Apple Numbers evaluate the same way are used, so the formulas survive every download format.

How do you use it?

On the Inputs tab, enter the water temperature, flow rate, internal diameter and pipe length.
Choose the pipe material from the list, or type a roughness override.
Enter the number of each fitting and valve in the fittings table.
Read the velocity, flow regime, friction factor, total head loss and pressure drop.
Open the Diameters tab to compare the same flow in nine standard sizes.

What is it good for?

Choosing a pipe size for a water supply or cooling loop
Estimating pump head for a short run with fittings
Comparing 1-inch and 2-inch pipe at the same flow
Checking velocity against a design limit

Questions about this sheet

Why does the sheet use Swamee-Jain instead of Colebrook?

Swamee-Jain gives the friction factor directly, so no iteration is needed. It agrees with Colebrook within 2% above a Reynolds number of about 12,000, and within 3% from 5,000 upward.

What does the transitional flow warning mean?

Between Reynolds numbers of 2,300 and 4,000 the flow can be laminar or turbulent. The sheet uses the turbulent equation there and marks the result as approximate.

Is the diameter the nominal size?

No. Enter the internal diameter in millimetres. The Diameters tab lists typical internal diameters for standard steel sizes.

Does it handle fluids other than water?

Not in this version. The properties are for water at atmospheric pressure, between 0 and 100 °C.