Roof Rafter Framing Calculator

Rafter Framing Calculator is a rafter length calculator and roof framing calculator built for carpenters, roofers, and framers - fast, accurate rafter math for common rafters, hip and valley rafters, birdsmouth cut angles, layout spacing, and pitch conversion, right on the job site.

Enter a building span and roof pitch and get rafter length, cut angles, and layout counts in decimal inches, feet-inches-fraction (to the nearest 1/16"), or metric.

CORE TOOLS

Common Rafter
Enter building span, roof pitch (rise per 12" or degrees), ridge board thickness, and overhang. Get rafter line length, total length with overhang, rise, plumb cut angle, and level (seat) cut angle - the two angles that lay out a birdsmouth notch.

Hip / Valley Rafter
Same span and pitch as your common rafter, plus hip or valley rafter length and plumb cut angle for a 45-degree layout.

Rafter Layout
Enter wall or ridge length and pick a standard on-center spacing (12", 16", 19.2", or 24"). Get rafter count per side, total rafter count, and a starting board quantity estimate.

Pitch Converter
Convert between x/12 pitch, degrees, and percent slope. Edit any field and the other two update instantly.

Saved Cut Sheets
Name and save a calculation to recall later - span, pitch, and results are stored right on your device.

BUILT FOR THE JOB SITE
- Feet-inches-fraction results rounded to the nearest 1/16", the resolution of a tape measure
- Decimal inches and metric (mm/cm/m) shown alongside every result
- Works without an internet connection
- No account required

This app is ad-supported. Saving a cut sheet may show a short video ad; if no ad is available your cut sheet still saves.

Rafter math depends on accurate field measurements and sound framing practice - always verify critical cuts, including birdsmouth depth, against your plans and local building code before cutting.

Whether you need a quick rafter length calculator, a roof framing calculator for hip and valley layouts, or a construction calculator that handles pitch conversion on the fly, this app gives you the numbers fast.