About this calculator

Roof pitch is the slope of a roof. In the US it's quoted as 'rise over 12' (e.g. 6/12). Elsewhere it's degrees or a ratio. Enter any one and the rafter length is derived from the half-span.

How it works

Enter your rise and run (half-span). The result updates as you type, using the formula shown below. Nothing you enter is stored.

Limits

Quantities assume regular shapes and standard waste allowances. Structural work still needs an engineer and Building Regulations sign-off.

Who it's for

DIY builders, site managers and tradespeople ordering materials or checking a take-off.

Formula: Angle = arctan(rise / run); Rafter = √(rise² + run²)

Frequently asked questions

What does the Roof Pitch Calculator do?

Convert roof pitch between rise/run, degrees and ratio. Get rafter length from span. Roof pitch is the slope of a roof. In the US it's quoted as 'rise over 12' (e.g. 6/12). Elsewhere it's degrees or a ratio. Enter any one and the rafter length is derived from the half-span.

Is the Roof Pitch Calculator free to use?

Yes. Every calculator on Calcurly.com is free, works in your browser without sign-up, and can be embedded on your own website.

How accurate is the Roof Pitch Calculator?

Results are calculated in real time using the formula Angle = arctan(rise / run); Rafter = √(rise² + run²). Treat the output as a well-informed estimate — always cross-check with local regulations, product datasheets, or a qualified construction & building professional before committing to a purchase or a job.

What inputs does the Roof Pitch Calculator need?

Enter values for: Rise, Run (half-span). Sensible defaults are pre-filled where possible so you can start with a single change.

Can I embed the Roof Pitch Calculator on my own website?

Yes — copy the iframe snippet at the bottom of this page, or use the Embed Generator to customise the size. The embedded version stays in sync with the live calculator on Calcurly.com.