Roof measurements · Updated November 3, 2026
Roof pitch area calculator
Convert the horizontal plan area of rectangular roof planes to estimated sloped surface area using a measured rise and run. Includes a user-entered count of identical planes.
Estimate sloped surface area for one or more identical rectangular roof planes. Measure the horizontal plan length and width for one plane in feet, then enter the vertical rise and horizontal run that define its pitch in the same units (for example, inches). The calculation runs in your browser and is a geometry estimate, not structural advice.
Enter values and calculate.
Rise and run may use inches or another matching unit because only their ratio is used. Enter each plane's horizontal projected dimensions, not the already sloped surface dimensions.
Sources and method
- U.S. Department of Energy: Homeowner’s Guide to Solar (reviewed November 3, 2026): notes that roof size, shape and slope are factors in evaluating a roof. This calculator estimates geometry only; it does not assess suitability.
For one rectangular plane, slope factor = √(run² + rise²) ÷ run. Sloped area = horizontal projected plan area × slope factor; for multiple identical planes, multiply the one-plane result by the entered plane count. Measure each differently shaped or pitched section separately. This estimate does not account for hips, valleys, dormers, overhangs, or openings, and is not a structural or installation recommendation.
How it works
Measure the horizontal projected length and width for one rectangular roof plane. Enter the rise and run that define its pitch in the same units, then enter how many identical planes to include. For unlike roof sections, calculate each separately and add their results.
Good to know
Quick answer: how do I calculate sloped roof area from a plan measurement and pitch?
Find the slope factor from the pitch: square root of (run squared plus rise squared), divided by run. Multiply one plane’s horizontal projected plan area by that factor, then multiply by the number of identical planes. The result estimates rectangular sloped surface area; irregular sections require separate measurements. Reviewed November 3, 2026.
What units should I use for rise and run?
Use matching units for rise and run, such as inches for both. The calculator uses their ratio, so that ratio is unitless. Enter plan length and width in feet.
Can I enter the whole house footprint for a gable roof?
Only if the total projected area can be represented by the entered identical rectangular planes at the same pitch. For a typical symmetric gable, that means entering the horizontal projection of one roof face and setting the plane count to two. Measure different pitches or shapes separately.
Does this include overhangs, dormers, hips or valleys?
No. The estimate models identical rectangular planes. Measure those features or differently shaped sections separately; this is not a complete roofing takeoff, structural calculation or installation recommendation.
Does the calculator recommend a roof pitch?
No. It only converts entered dimensions to geometric surface area. The Department of Energy notes that roof size, shape and slope are factors in roof evaluation; a project-specific assessment requires appropriate professional guidance.
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