Plumbing Pipe Length & Fittings Calculator

Inputs

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Unit system *

Nominal diameter (mm) *

Extra allowance (%)

Segments

Add straight runs. Use the selected length unit.

Label	Length	(m)

Fittings

Enter counts. Equivalent lengths use D-multiples; see table below.

Pressure Drop Add-On

Method

Length basis

Flow rate

Material (C-factor)

C-factor (override)

Leave blank to use preset value.

Results

Straight length0.000 m

Equivalent length (fittings)0.000 m

Developed length0.000 m

Cut length (incl. allowance)0.000 m

All values shown in meters.

Pressure Drop

Velocity0.000 m/s

Reynolds number0

Friction factor f—

Headloss per 1000.000 m / 100 m

Headloss over length0.000 m

Pressure drop0.00 kPa

Method: Hazen-Williams, length basis: developed.

Equivalent length factors (×D)

Fitting	×D

Values are typical approximations. For critical work, use manufacturer data.

Example data

Segment	Length	Unit
Water heater to tee	6.0	m
Tee to sink	3.4	m
Tee to shower	4.2	m

Counts: 90° elbows=6, 45° elbows=2, tee-through=1, tee-branch=1, gate valves=2.
Diameter: 25 mm; allowance: 5%.
Flow example: 0.8 L/s; C=140 (copper) or ε=0.045 mm (steel).

Formula used

Developed length L_dev = ΣL_straight + Σ(n_i · k_i · D)

Cut length L_cut = L_dev · (1 + allowance/100)

Hazen-Williams (SI): h_f = 10.67 · L · Q^1.852 / (C^1.852 · d^4.87)

Darcy-Weisbach: h_f = f · (L/D) · v²/(2g), where f from Swamee-Jain for turbulent; f=64/Re for laminar.

We compute in SI internally and convert to display units; defaults use water at ~20 °C.

How to use

Select the unit system.
Enter nominal pipe diameter.
Add each straight segment with its length.
Enter counts for fittings used along the run.
Set an allowance percentage for waste or trimming.
Choose pressure-drop method, flow rate, and material preset.
Press Compute totals and export CSV or PDF.

FAQs

They are equivalent lengths expressed as multiples of pipe diameter. For example, 30×D means thirty diameters of additional length.

No. Factors and friction vary by material, schedule, radius, and manufacturer. Use this for planning; consult product data for critical calculations.

Hazen-Williams is common for water in typical building systems. Darcy-Weisbach is general-purpose and handles any fluid when density, viscosity, and roughness are known.

Choose metric or imperial. Segment lengths, diameter, flow, and outputs adapt automatically and convert consistently.

We treat the entered diameter as internal. If you’re using nominal sizes, enter the actual internal diameter for best accuracy.

Fittings Contribution Report

Fitting	Count	×D	Equivalent length

This report multiplies each fitting count by its ×D and current diameter.

Material Coefficients & Roughness Reference

Material	Hazen-Williams C	Roughness ε	ε unit

Values are typical. Choose the closest preset, or override C/ε above for your system.

Flow–Velocity–Headloss Reference

Flow	Velocity	Headloss / 100

Computed with current diameter, method, and material presets at standard conditions.