Roofing Calculator

About the Roofing Calculator

Calculates the actual sloped roof area from the building footprint and roof pitch, then the number of roofing squares and bundles needed.

How to use this calculator

1. Enter the roof footprint area, usually the horizontal area of the building in square feet or square meters.
2. Enter the roof pitch as the angle or slope value used by the calculator.
3. Check the calculated roof area, which is larger than the footprint because of the slope.
4. Use the result to estimate material needs, then add a little extra for cuts, overlaps, and waste.

The formula explained

The formula computes the sloped roof area from the flat footprint area and the roof pitch. It uses the cosine of the pitch to scale the footprint up to the actual surface area.

• roof area = the total sloped surface area of the roof
• footprint = the horizontal area covered by the building
• pitch = the roof pitch entered into the calculator, usually as an angle
• cos(pitch) = the cosine of the pitch value used to adjust for slope

Step by step method

1. Start with the footprint area and the pitch value.
2. Compute \(\cos(pitch)\), then take its reciprocal by finding \(\frac{1}{\cos(pitch)}\).
3. Multiply the footprint by \(\frac{1}{\cos(pitch)}\) to get the roof area.

Worked example

Problem. A house has a footprint of \(1{,}800\) square feet and a roof pitch of \(30^\circ\). Find the roof area.

1. Use the formula \(roof\ area = footprint \times \frac{1}{\cos(pitch)}\).
2. Substitute the values, \(roof\ area = 1{,}800 \times \frac{1}{\cos(30^\circ)}\). Since \(\cos(30^\circ) \approx 0.866\), calculate \(1{,}800 \times \frac{1}{0.866}\).
3. The roof area is about \(2{,}078\) square feet.

Tips and common mistakes

• Make sure the pitch is entered in the same form the calculator expects, because degrees and slope ratios are not the same thing.
• Remember that the roof area is larger than the footprint, so you may need extra material for waste and overlaps.

Frequently asked questions