---
title: "Roof pitch calculator — free, runs in your browser"
description: "Convert between roof pitch in degrees, ratio and percentage, and get rafter length. Free, no sign-up, and nothing you enter leaves your browser."
url: https://atoneplace.net/tools/roof-pitch-calculator/
site: "At One Place"
---

# Roof pitch calculator

Convert between roof pitch in degrees, ratio and percentage, and get rafter length.

## How it works

Converts roof pitch between the three ways it gets expressed \u2014 degrees, a rise-over-run ratio, and a percentage \u2014 and calculates the rafter length for a given span.

The ratio conventions differ by country and are a genuine source of confusion. In the United States pitch is written as rise in inches per 12 inches of run, so 6:12 means six inches of rise per foot, or 26.6 degrees. In much of Europe it is stated in degrees directly, and in road and drainage work as a percentage, where 100% is 45 degrees rather than vertical.

Rafter length is the hypotenuse: the square root of rise squared plus run squared. It is always longer than the run, which is why roof area exceeds the footprint of the building \u2014 a 30-degree roof has about 15% more surface than the floor beneath it, and that matters when ordering covering.

> This tool runs entirely in your browser. Nothing you enter is sent to a server, logged or stored, and the page keeps working with the network disconnected.

## Common questions

### What does a 6:12 roof pitch mean?

Six units of rise for every twelve of run \u2014 26.6 degrees. It is the common American way of writing pitch.

### How do you convert roof pitch to degrees?

Take the arctangent of rise divided by run. A 6:12 pitch is arctan(6/12) = 26.57 degrees.

### Is roof area the same as floor area?

No, it is always larger. A 30-degree pitch adds about 15% and a 45-degree pitch about 41%.

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## Sources

- Calculated on this page — At One Place (/about/)