Home and Construction
Rafter Length Calculator
Rafter Length Calculator calculate common-rafter length, roof angle, vertical rise, and slope factor from horizontal run, pitch, and overhang.
Home and Construction
Rafter Length Calculator
Calculate common-rafter length, roof angle, vertical rise, and slope factor from horizontal run, pitch, and overhang.
Formula
Rafter length = total horizontal run x sqrt(1 + (pitch rise / 12)^2).
About the Rafter Length Calculator
Calculate common-rafter length, roof angle, vertical rise, and slope factor from horizontal run, pitch, and overhang. This tool keeps the requested measurements separate and applies the named method instead of substituting an unrelated general estimate.
How the Rafter Length Calculator Works
The horizontal run to the ridge and horizontal overhang are combined, while pitch in inches per 12 inches supplies the right-triangle slope.
Formula
Rafter length = total horizontal run x sqrt(1 + (pitch rise / 12)^2).
The calculation runs in your browser. Values are validated for required ranges, compatible units, and method-specific restrictions before results are displayed.
Required Inputs
- Wall to ridge horizontal run (required) - enter in ft.
- Roof pitch rise per 12 (required) - enter in in.
- Horizontal overhang (required) - enter in ft.
Results Reported
The result panel reports the final answer and the intermediate quantities needed to check the calculation:
- Sloped rafter length (ft)
- Roof angle (deg)
- Vertical rise to ridge (ft)
- Slope factor
- Sloped overhang tail (ft)
Rafter Length Calculator Example
Select Example Data in the calculator to load this reproducible input set:
| Input | Example value |
|---|---|
| Wall to ridge horizontal run | 12 ft |
| Roof pitch rise per 12 | 6 in |
| Horizontal overhang | 1.5 ft |
How to Use the Calculator
- Confirm that the calculator title and formula match the quantity you need.
- Enter every required value using the unit shown with its field.
- Select Example Data to inspect a valid input set, or enter your own values and select Calculate.
- Review all reported values and the displayed formula before using the answer.
- Use Copy Result or Download CSV when you need a reusable record.
Accuracy and Limitations
This geometric length excludes ridge, birdsmouth, fascia, seat-cut, and code adjustments. Structural member sizing requires local span tables or engineering.
Keep units consistent, use measurements that represent the actual situation, retain full precision during the calculation, and round only the final answer. Professional decisions may require current official rules, field measurements, laboratory methods, or specialist review.
Frequently Asked Questions
What does the Rafter Length Calculator calculate?
Calculate common-rafter length, roof angle, vertical rise, and slope factor from horizontal run, pitch, and overhang.
Which formula does the Rafter Length Calculator use?
Rafter length = total horizontal run x sqrt(1 + (pitch rise / 12)^2). The horizontal run to the ridge and horizontal overhang are combined, while pitch in inches per 12 inches supplies the right-triangle slope.
How should I use the Rafter Length Calculator result?
This geometric length excludes ridge, birdsmouth, fascia, seat-cut, and code adjustments. Structural member sizing requires local span tables or engineering.