Home Improvement chart
Roof Pitch and Rafter Length Chart
Use this roof-pitch chart to compare slope multipliers and basic rafter length for a 12-foot horizontal run before adding overhangs, cuts, and structural requirements. Use the chart as a quick planning reference, then use Roof Pitch Rafter Length Calculator when you need exact numbers for your own inputs.
At a glance
- Coverage
- 10 reference rows
- Default schedule
- See assumptions below
- Data effective
- Not stated
- Published
- Not stated
- Updated
- Not stated
- Author
- EverydayCalc.org
- Reviewer
- EverydayCalc editorial review
Chart values
| Roof pitch | Slope multiplier | Length per 12 ft run |
|---|---|---|
| 2:12 | 1.014× | 12.17 ft |
| 3:12 | 1.031× | 12.37 ft |
| 4:12 | 1.054× | 12.65 ft |
| 5:12 | 1.083× | 13.00 ft |
| 6:12 | 1.118× | 13.42 ft |
| 7:12 | 1.158× | 13.89 ft |
| 8:12 | 1.202× | 14.42 ft |
| 9:12 | 1.250× | 15.00 ft |
| 10:12 | 1.302× | 15.62 ft |
| 12:12 | 1.414× | 16.97 ft |
Calculated from the existing roof pitch and rafter length calculator formula. Use approved plans and local structural requirements for the final member and cuts.
How to use this chart
Match the roof rise per 12 inches of horizontal run, then multiply the actual horizontal run by the slope multiplier. Use the calculator for a different run, overhang, or cut allowance.
When to use the calculator instead
Use the calculator when your measurements, rates, room conditions, local prices, tank setup, loan terms, or classroom routine do not match the simple chart rows. The calculator lets you adjust the inputs instead of forcing your situation into a rough example.
Examples from this chart
Worked example
A 6:12 roof over a 12-foot horizontal run has a basic slope length of about 13.42 feet. Overhangs, ridge details, birdsmouth cuts, bearing, connections, and structural sizing remain separate.
Limitations and assumptions
The multiplier is sqrt(12² + rise²) ÷ 12, and the example length uses a 12-foot horizontal run. Rows describe geometry only and do not size or approve a rafter.
Save or share this chart
You can print this page, save the tall image for planning, or link to the page from a blog post, classroom resource, forum answer, or project checklist so readers can open the calculator too.
Chart questions
Chart questions
Does the rafter chart include overhang?
No. Add the measured horizontal overhang and any cut allowance separately in the calculator.
Does this chart tell me what rafter size to use?
No. Species, grade, spacing, span, loads, bearing, connections, cuts, and local code require approved structural design.