📐 Rafter Length Calculator
Calculate rafter lengths, birdsmouth cuts, and lumber requirements
Roof Specifications
Rafter Terms
Run: Horizontal distance from wall plate to ridge
Rise: Vertical height from wall plate to ridge
Plumb Cut: Vertical cut at ridge end
Birdsmouth: Notch cut where rafter sits on wall
Tail: Rafter extension past the wall (overhang)
HAP: Height of rafter remaining above wall plate
Roof Pitch Reference Table
| Pitch | Angle | Factor | Description |
|---|---|---|---|
| 3:12 | 14.0° | 1.031 | Low slope - minimum for shingles |
| 4:12 | 18.4° | 1.054 | Standard minimum |
| 5:12 | 22.6° | 1.083 | Common residential |
| 6:12 | 26.6° | 1.118 | Standard residential |
| 8:12 | 33.7° | 1.202 | Steep - good snow shedding |
| 12:12 | 45.0° | 1.414 | Very steep - walkable limit |
Factor: Multiply run by this factor to get rafter length (without overhang)
⚠️ Important Disclaimer
This calculator provides theoretical dimensions for planning purposes. Actual rafter sizing depends on lumber species, grade, span, load requirements, and local building codes. Always verify calculations with a structural engineer and obtain necessary building permits. Use appropriate safety equipment when working at heights.
About Rafter Length Calculator - Roof Rafter Dimensions
Calculate rafter lengths, birdsmouth cuts, and angles. Determine lumber needs for roof rafter construction.
Rafter Length Calculator - Roof Rafter Dimensions is a powerful online utility designed to help you process images quickly and securely. You can combine this with our Image Compressor for a complete workflow.
Our tools run entirely in your browser, ensuring your data remains private. No uploads, no waiting, just instant results. For more creative options, try the Collage Maker.
Perfect for quick edits, format changes, and optimizations without opening heavy desktop software. If you need to change dimensions, use the Image Resizer.
Key Features
Why Use This Tool?
How to Use
Upload your image
Apply desired changes
Download result