When to use this calculator
Express a roof slope in the familiar rise-in-twelve convention. Use matching units for rise and run; the result is a ratio numerator, not degrees.
Explore the material quantities calculators for other questions in this topic. For a related calculation, use the Roof Ridge Cap Calculator: Estimate ridge-cap pieces using installed linear coverage.
PUTTING IT INTO PRACTICE
Roof Pitch Ratio: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Roof rise | 3 |
| Horizontal run | 6 |
| Result | 6 rise per 12 run |
- Check the input labels and enter the example values above.
- Apply the relationship: Rise per 12 run = 12 × rise/run.
- The result is 6 rise per 12 run, rounded for display.
How to interpret your result
Use matching units for rise and run; the result is a ratio numerator, not degrees.
Calculate net geometric quantities first, then apply a project-specific allowance where appropriate. Coverage per bag or pack should come from the product label. Bulk density, trimming and compaction can substantially change order quantities.
Frequently asked questions
Does a geometric estimate include waste automatically?
Only when a waste or allowance input is provided. Otherwise add an appropriate allowance separately before ordering.
When is the roof pitch ratio calculator useful?
Express a roof slope in the familiar rise-in-twelve convention. Use matching units for rise and run; the result is a ratio numerator, not degrees.
How do I use the roof pitch ratio calculator?
Enter roof rise, horizontal run. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Rise per 12 run = 12 × rise/run.
What should I check before using the result?
Use matching units for rise and run; the result is a ratio numerator, not degrees.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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