# Pipe Pressure Drop Calculator (Darcy-Weisbach)

Compute the Darcy-Weisbach major (friction) pressure drop in a straight pipe: ΔP = f·(L/D)·(ρ·v²/2) Pa and head loss h_f = f·(L/D)·v²/(2g) m. The user supplies the Darcy friction factor f (not the Fanning factor). Length in m/km/ft, diameter in m/cm/mm/inch, density in kg/m³/g/cm³/lb/ft³ — all normalised to SI internally. Returns ΔP in Pa, kPa and bar, and head loss in m and ft. Gravity defaults to 9.81 m/s² and may be overridden.

> Canonical page: https://elysiatools.com/en/tools/pipe-pressure-drop-darcy

- **Category:** Math & Numbers

- **Keywords:** Darcy-Weisbach, pressure drop, head loss, friction loss, major loss, pipe flow, friction factor, Darcy friction factor, Moody chart, fluid mechanics, hydraulics, pressure drop, pipe

## 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.

## Inputs

- **Friction Factor f (Darcy)** (number): Darcy friction factor f (also called Moody / Darcy-Weisbach factor). NOTE: this is NOT the Fanning friction factor (f_Darcy = 4·f_Fanning). Obtain f from a Moody chart or the Colebrook-White correlation.
- **Pipe Length L** (number): Pipe length L in the selected Length Unit.
- **Length Unit** (select)
- **Diameter D** (number): Internal pipe diameter D in the selected Diameter Unit.
- **Diameter Unit** (select)
- **Density ρ** (number): Fluid density ρ in the selected Density Unit.
- **Density Unit** (select)
- **Velocity v** (number): Mean flow velocity v in m/s.
- **Gravity g** (number): Gravitational acceleration g in m/s². Default 9.81 (Earth); override for non-Earth or unit-head conversions.
- **Decimal Places** (number)

## 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

- Enter the Darcy friction factor f, pipe length, internal diameter, and mean flow velocity.
- Select supported units for length, diameter, and fluid density; values are normalized to SI internally.
- The calculator applies ΔP = f·(L/D)·(ρ·v²/2) and uses gravity to calculate head loss.
- Review 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.

## Frequently asked questions

### 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.

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