Roofing Calculator

Created by Bogna Szyk
Reviewed by Steven Wooding and Jack Bowater
Last updated: Oct 27, 2021

The roofing calculator allows you to determine the area of the gable or shed roof of your house and to accurately estimate its cost. All you have to know are the dimensions of your house and the roof pitch, and this roof cost calculator will do the rest for you. Let's get started!

How do you calculate the roof area?

  1. Begin with calculating the area of your house in a plane parallel to the ground. If your house is rectangular, all you need to do is multiply the length and width of the building. If the shape of your house is more complex, simply enter the total area (after measuring the exterior dimensions) into the appropriate box.

  2. Determine the roof pitch of your house. Roof pitch is the slope created by the rafters. If you don't know how to calculate it, head to our roof pitch calculator. You can input it either in degrees, as a percentage or as a ratio of x:12.

  3. Once you know these values, you will be able to calculate the roof area. Begin by converting the roof pitch to an angle expressed in degrees, using the following formulas:

    pitch(%) = x / 12 * 100%

    pitch(deg) = arctan[pitch(%)]

  4. Then, use the following equation to find the total area of the roof:

    roof area = base area / cos[pitch(deg)]

Estimating the cost of the roof

Once you know the area of the roof, you have to decide on the scope of works. Do you want to build the roof from scratch, or maybe replace the old layers? You also need to decide on the finishing material. For example, asphalt shingles will be less expensive than clay tiles.

After you've made all of these decisions, it's best to contact your local contractor and ask about the cost of both materials and labor per square meter or square foot of roof area. Remember that this unit price should include all additional elements such as fasteners, as well as the cost of removing all layers and disposing of them (if applicable).

The most typical cost of roofing falls between $2 and $4 per square foot (including labor). If the price proposed by your contractor deviates from these values, it is advisable to check with other contractors before starting the works.

If you cannot contact any contractor, calculate the cost of materials (for example by going to the nearest construction store) and multiply this price by 2.5. You will obtain an approximate price including labor, assuming that 40% of the cost is taken by the materials and 60% by the labor.

The last thing you have to do is to multiply this cost by your roof area and voilà, you now know the total cost of your roof! Remember that the real cost might differ from this value a bit due to waste, so plan ahead and assign more funds to this construction work.

If you are not on a tight budget, maybe you'd like to add solar panels? ☀️

Also, make sure to take a look at our concrete slab cost calculator, too!

Bogna Szyk
House dimensions
House length
ft
House width
ft
House base area
ft²
Roof pitch (enter any one value)
Roof pitch
deg
Roof pitch (%)
%
Roof pitch (x:12)
:12
Roof cost
Roof area
ft²
Unit price
$/
ft²
Total cost
$
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