Roofing Calculator

Estimate the true area of a slanted roof and the amount of materials necessary to construct or replace it. Never climb on a dangerous roof to measure it again—just use your house base area and pitch!

Roof Geometry

House Base Area (sq ft)

Roof Pitch (/12)

/ 12

Materials & Cost

Wastage %

Price per Square $

1 Square =
100 sq ft

Results

Squares Needed

Slope Multiplierx 1.118

True Roof Area2236.07 sq ft

+ 10% Wastage2459.67 sq ft

Estimated Cost$3,000.00

Roofing Expert Guide

What is Roof Pitch?

Roof pitch is the measurement of a roof's vertical rise divided by its horizontal run. It is often compared to slope. In the United States, a run of 12 inches (1 foot) is standard. For instance, a 6/12 roof pitch means that the roof rises 6 inches vertically for every 12 horizontal inches.

Roof pitch affects walkability, drainage, and material choices. Roofs in areas with heavy rain or snowfall tend to have steeper pitches to shed water quickly.

Slope Correction Factors

A slanted roof has more surface area than the flat footprint of the house beneath it. To find the "True Roof Area", you must multiply the horizontal base area by a Correction Factor.

2/12 Pitch: × 1.014
4/12 Pitch: × 1.054
6/12 Pitch: × 1.118 (Most Common)
9/12 Pitch: × 1.250
12/12 Pitch (45°): × 1.414

Our calculator automatically applies the precise trigonometric math to determine your exact slope correction multiplier based on your input.

What is a Roofing "Square"?

In the roofing and siding industries in North America, materials are not sold by the individual square foot. They are sold in units called "Squares".

1 Roofing Square = 100 Square Feet

For example, if your true roof area (including 10% wastage) is 2,450 sq ft, you will need to purchase exactly 25 Squares of shingles from the supplier.