MeasureHaven

Roofing

Roof area calculator

Convert a horizontal roof footprint into pitched surface area and roofing squares.

Your project

ft
ft
%
Extra material for cuts, spillage or irregular edges. Adjust for your project.
Optional. Enter your supplier’s price; 0 leaves cost out.

YOUR ESTIMATE

Enter your measurements and select Calculate estimate.

Planning estimate only. Confirm the product’s coverage and your measurements before ordering.

How to use this estimate

The footprint is the horizontal projection of the whole roof, including overhangs. Do not enter sloped rafter length as a footprint dimension. For a simple gable roof, using the full footprint already accounts for both sides: do not double the result. Separate roofs with different pitches into independent sections.

The calculation

Roof surface area = horizontal footprint area × √(1 + (rise / run)²). One roofing square = 100 ft².

A worked example

A 40 × 30 ft roof footprint at 6:12 pitch has 1,341.64 ft² of surface. At 10% waste, allow 1,475.80 ft², or 14.758 roofing squares.

For a uniform-pitch rectangular projected footprint. Dormers, intersecting planes and complex geometry need a measured takeoff. Never climb onto a roof solely to use this calculator.

Common questions

Is my house floor area the roof footprint?

Not necessarily. Multiple stories, overhangs, porches and extensions can make floor area a poor substitute for the roof’s horizontal projection.

References & method

Inch Calculator roofing reference. See how we check calculations. Reference links provide context; no supplier endorses this site.