# Pipe Friction Factor Calculator (Colebrook-White / Haaland)

Compute the Darcy friction factor: laminar closed-form f=64/Re for Re<2000, or iterative Colebrook-White solution for transitional/turbulent flow, with the explicit Haaland approximation always returned as a cross-check. Reports relative roughness ε/D, absolute roughness (m), diameter (m), flow regime (laminar/transitional/turbulent), effective method and iteration count. Roughness ε in m/mm/µm, diameter D in m/cm/mm.

> Canonical page: https://elysiatools.com/en/tools/pipe-friction-factor

- **Category:** Math & Numbers

- **Keywords:** Darcy friction factor, friction factor, Colebrook, Colebrook-White, Haaland, pipe roughness, relative roughness, Reynolds number, laminar, turbulent, transitional, fluid mechanics, pipe flow, pressure drop, Darcy-Weisbach, hydraulics

## Overview

The Pipe Friction Factor Calculator computes the Darcy friction factor from Reynolds number, pipe roughness, and internal diameter. It uses f=64/Re for laminar flow and Colebrook-White iteration for higher Reynolds numbers, while also returning a Haaland estimate for comparison.

## Inputs

- **Reynolds Number Re** (number): Reynolds number Re = ρ·v·D/μ. Must be positive.
- **Roughness ε** (number): Absolute pipe roughness ε in the selected unit. 0 = perfectly smooth.
- **Roughness Unit** (select)
- **Diameter D** (number): Internal (hydraulic) pipe diameter D in the selected unit.
- **Diameter Unit** (select)
- **Method** (select): Auto = laminar formula if Re<2000, else Colebrook. Haaland estimate is always reported as a cross-check.
- **Decimal Places** (number)

## When to use

- Estimate the Darcy friction factor for a pipe-flow calculation.
- Compare iterative Colebrook-White and explicit Haaland results for turbulent flow.
- Check how pipe roughness, diameter, and Reynolds number affect the flow regime and relative roughness.

## How it works

- Enter a positive Reynolds number, absolute roughness, and internal pipe diameter.
- Select roughness and diameter units: m, mm, or µm for roughness, and m, cm, or mm for diameter.
- Choose Auto, Colebrook (iterative), or Haaland (explicit) as the calculation method.
- Review the Darcy friction factor, Haaland cross-check, relative roughness, flow regime, effective method, and iteration count.

## Use cases

- Pipe-flow and fluid-mechanics calculations requiring a Darcy friction factor.
- Hydraulic comparisons between smooth and rough pipes using relative roughness.
- Engineering checks that compare Colebrook-White results with the Haaland approximation.

## Frequently asked questions

### What does this calculator return?

It returns the Darcy friction factor, relative roughness, flow regime, effective method, and iteration count. A Haaland estimate is also provided as a cross-check.

### Which formula is used for laminar flow?

For Re<2000, the calculator uses the closed-form relation f=64/Re.

### How does Auto mode choose the method?

Auto uses the laminar formula when Re<2000 and Colebrook-White otherwise. The Haaland estimate is still reported for comparison.

### Can I calculate friction for a smooth pipe?

Yes. Enter roughness as 0 to represent a perfectly smooth pipe.

### What inputs are required?

Reynolds number, absolute roughness, and internal pipe diameter are required. Unit selections, method, and decimal places are optional.

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