Pipe Pressure Drop Calculator (Darcy-Weisbach)

Pipe Pressure Drop Calculator (Darcy-Weisbach) | Online Free Tool | Elysia Tools

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Math & Numbers
Input types: number, select
Output type: json
Sample coverage: 4
API ready: Yes

Overview

The Darcy-Weisbach pipe pressure drop calculator estimates major friction loss in a straight pipe using the Darcy friction factor, pipe length, internal diameter, fluid density, and mean velocity. It returns pressure drop in Pa, kPa, and bar, plus head loss in meters and feet.

When to use

Estimate friction pressure drop in a straight water, oil, or other fluid pipeline.
Compare how pipe length, diameter, density, or velocity affects head loss.
Convert a Darcy-Weisbach result into pressure and head-loss units for hydraulic calculations.

How it works

1Enter the Darcy friction factor f, pipe length, internal diameter, and mean flow velocity.
2Select supported units for length, diameter, and fluid density; values are normalized to SI internally.
3The calculator applies ΔP = f·(L/D)·(ρ·v²/2) and uses gravity to calculate head loss.
4Review pressure drop in Pa, kPa, and bar, along with head loss in meters and feet.

Use cases

Sizing and reviewing straight pipeline sections in hydraulic systems.
Estimating water or oil friction losses from known flow velocity and pipe geometry.
Checking pressure-drop and pump-head calculations using consistent engineering units.

Examples

1. Water pipeline friction loss

Hydraulic engineer

Background

An engineer is checking the friction loss in a 100 m water pipe with a 50 mm internal diameter and a mean velocity of 2 m/s.

Problem

Calculate the Darcy-Weisbach pressure drop and corresponding head loss for the straight pipe section.

How to use

Enter the Darcy friction factor, pipe length, diameter, water density, velocity, and default gravity.

f = 0.02; L = 100 m; D = 0.05 m; ρ = 1000 kg/m³; v = 2 m/s; g = 9.81 m/s²

Outcome

The calculator returns a pressure drop of 80,000 Pa, or 80 kPa and 0.8 bar, with a head loss of 8.1549 m or 26.7551 ft.

2. Oil pipeline pressure drop

Process engineer

Background

A process engineer needs to estimate friction loss for oil flowing through a 50 m pipe with a 0.1 m internal diameter.

Problem

Determine the pressure drop and head loss using the oil density, velocity, and Darcy friction factor.

How to use

Enter the oil density as 850 kg/m³, set the pipe dimensions and velocity, and use the default gravity value.

FAQ

What friction factor should I enter?

Enter the Darcy friction factor, also called the Moody or Darcy-Weisbach factor. Do not enter the Fanning friction factor.

What type of pressure loss does this calculator calculate?

It calculates major friction loss in a straight pipe. It does not calculate minor losses from fittings, valves, or bends.

Which length units are supported?

Pipe length can be entered in meters, kilometers, or feet.

Which diameter units are supported?

Internal pipe diameter can be entered in meters, centimeters, millimeters, or inches.

What is the default gravity value?

Gravity defaults to 9.81 m/s², and you can override it when needed.

f = 0.018; L = 50 m; D = 0.1 m; ρ = 850 kg/m³; v = 1.5 m/s; g = 9.81 m/s²

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Water pipeline friction loss

2. Oil pipeline pressure drop

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