Roofing Material Calculator

Enter the footprint of the building and the pitch multiplier for the roof. You get the sloped area, the squares to order and what they cost at your own supplier price. Nothing here is prefilled with a coverage or a rate.

Building length

Measured on the ground, along the eaves. Not up the slope.

Building width

The other side of the footprint, gable to gable. Add the overhangs if the roof carries them.

Measured in

Slope number (the pitch multiplier)

A sloped roof is bigger than the flat ground under it, and this number says how much bigger. Get yours from the Roof Pitch calculator. A roof that rises 6 inches for every 12 inches across is 1.118, and one that rises 10 in 12 is 1.302. Type 1 only for a truly flat deck.

Waste allowance

Cuts, starter course, valleys, hips and breakage. Your own figure from your own roofs: nothing is added for you, and left at 0 this is the bare area with nothing spare.

Result

Fill in a few more boxes and the answer will show here.

Opens your print dialog. Choose Save as PDF. Your figures stay on this device.

Loading the calculator.

This is a general measurement calculator. Confirm dimensions, product coverage and job requirements before ordering or installing materials.

From a footprint to a roofing order

Roofing is bought in squares, and a square is one hundred square feet of finished roof. That definition is fixed, which makes the whole order a chain of three multiplications: the footprint of the building, the pitch multiplier that turns that flat area into sloped surface, and whatever allowance you add on top for cuts and breakage. Divide by a hundred and you have squares. Everything else (bundles, rolls, caps) comes off figures printed on the products you are actually laying.

The pitch multiplier is the input that decides whether the order is right. It scales every line below it, so being wrong about the slope is not a small rounding difference. It is the difference between finishing on Friday and waiting on a delivery with the deck open. Work it out properly in the Roof Pitch calculator and type the number in. This tool asks rather than assumes, because a guessed slope hidden inside a total is a guess nobody can check afterwards.

The mistake worth naming is double counting the pitch. Some measuring services and aerial reports already give you sloped area, not footprint. Feed one of those in here and multiply it again and you have bought a roof and a fifth. Read what the number on the report actually says before you use it.

Waste is a judgment, not a fact, which is why nothing is added for you. A plain gable eats far less than a roof full of valleys, hips and dormers. Keep your own figure, then check the order against what really got used. Zeus holds the receipts on the job they belong to, so next season's roofs are ordered from your own numbers rather than from habit.

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