How this worksheet works
From footprint to order area
Start with the horizontal footprint—the area the roof covers when viewed from above. The calculator applies the slope factor for the entered rise and run, then shows measured and waste-adjusted quantities separately.
How to use it
- Measure the horizontal footprint length and width in feet.
- Enter the roof rise and run. A 6-in-12 pitch rises 6 inches for every 12 inches of run.
- Choose a waste allowance and calculate. Review both the raw sloped area and order area.
Useful for
- Quick material takeoffs from plan dimensions
- Checking a supplier or estimator area figure
- Comparing the effect of pitch and waste
Assumptions
- A simple rectangular horizontal footprint
- One consistent pitch across the measured footprint
- Dimensions are horizontal, not measured along the slope
Limitations
- Does not subtract openings or add overhangs unless included in the footprint
- Complex roofs should be divided into planes and measured individually
- Waste is a planning allowance, not a field-verified cut list
Common checks
Questions about this calculator
What is the roof slope factor?
It is the multiplier that converts horizontal area to sloped area. It is calculated as the square root of rise² + run², divided by run.
Should overhangs be included?
Yes. If your footprint dimensions stop at the wall line, add the horizontal overhang before calculating.
How much waste should I use?
Waste depends on geometry, product, layout, and installer practice. Simple gables often need less than cut-up roofs; confirm the allowance with the installer and manufacturer.