Architect Tools

Roofing · Calculator

Rafter Length Calculator

Calculate common-rafter length from horizontal run, rise and eave overhang.

Project inputs

Enter your project values, then press Calculate.

How this calculator works

Calculate common-rafter length from horizontal run, rise and eave overhang.

rafter = √[(run + overhang)² + adjusted rise²]

How to use the Rafter Length Calculator

1. Enter project inputs

  • Horizontal run (m)
  • Vertical rise (m)
  • Horizontal overhang (m)

2. Review the results

  • Rafter length
  • Roof angle
  • Slope factor

3. Check the calculation

The calculator uses the following core relationship:

rafter = √[(run + overhang)² + adjusted rise²]

Estimating note: Actual material quantities can vary with site conditions, detailing, product dimensions, installation method, and waste.

Rafter Length Calculator FAQ

What does the Rafter Length Calculator calculate?

Calculate common-rafter length from horizontal run, rise and eave overhang.

What information do I need to use the Rafter Length Calculator?

The calculator uses inputs such as Horizontal run (m), Vertical rise (m), and Horizontal overhang (m). Use values from your drawings, measurements, product data, or project specifications.

How should I use the results from the Rafter Length Calculator?

Use outputs such as Rafter length, Roof angle, and Slope factor for estimating and cross-checking. Before purchasing or construction, confirm the dimensions, units, waste factors, supplier packaging, and project specifications.