The Roofing Calculator allows you to calculate the area of your house’s gable or shed roof and estimate its cost precisely. All you need are the measurements of your home and the pitch of your roof, and this roofing calculator will take care of the rest. Your roof is a major component of your house, and a successful reroofing projects require a large investment, both time and money. Since you cannot afford any mistakes during installation of your new roof, we highly recommend you hiring a professional contractor.

Furthermore, in the following text we will show how to calculate the roof area, estimate the cost, what is the roof pitch and how to use our calculator. If you are interested in construction, you should see some other posts in our construction section such as DIY Shed Cost Calculator. Also, check our Framing or Roof Pitch Calculator.

How do you calculate the roof area?

Begin by determining your home’s area on a plane parallel to the ground. If your house is rectangular, simply increase the length and breadth of the structure. If your house has a more complicated design, just put the entire area (after measuring the external measurements) into the relevant box. Next, determine the pitch of your home’s roof. The slope generated by the rafters is known as roof pitch. You can enter it in degrees, as a percentage, or a x:12 ratio.

You will be able to determine the roof area after this information. Start by translating the roof pitch into a degree angle using the following formulas:

Pitch [\%] =\frac {x} {12} \times 100 \%
Pitch \degree=\arctan(Pitch [\%])
Roof \; Area = \frac {Base \; Area} {\cos (Pitch \degree)}

The computed area is only a guess. When a roof has a complicated form, such as the one shown to the right, measuring the dimensions and areas of each portion of the roof to compute the overall area will yield a more accurate area measurement. The calculator cannot account for complicated forms based only on square footage measurements. In the United States, the most prevalent roofing materials are shingles, membrane roofing and ceramic tile, all of which have distinct life periods. Shingles normally last 15-30 years, whereas membrane roofing materials endure 5-15 years on average. Ceramic tile roofs are pricey, but they may last for more than a century.

Estimating the cost of the roof

After you’ve determined the size of the roof, you’ll need to decide on the scope of work. Do you want to start from the ground up or just replace the previous layers? You must also choose the finishing material. Asphalt shingles, for example, will be less costly than clay tiles for finishing material.

After you’ve made all of these selections including roofing material (shingles or tiles), call a local contractor to find out how much materials and labor cost you need per square meter or square foot of roof space. Remember that this unit price should include any extras like fasteners, as well as the cost of removing and disposing of all layers (if applicable). Roofing costs typically range between $2 and $4 per square foot (including labor). If your contractor’s price differs from these figures, it’s a good idea to get quotes from different contractors before commencing the work.

If you can’t find a contractor, figure out how much materials will cost (for example, by going to the local building supply store) and increase it by 2.5. You’ll get an estimate for the whole cost, including labor, assuming that materials account for 40% of the cost and labor for 60%. The next step is to multiply this cost by the area of your roof, and voila, you have the entire cost of your roof! Remember that due to waste, the actual cost may fluctuate somewhat from this estimate, so plan ahead and allocate additional finances to your building project.

Roof Pitch

Roof pitch is calculated by dividing a roof’s vertical rise by its horizontal run. Although it is sometimes likened to slope, it is not the same. A run of 12 inches (1 foot) is used in the United States, and pitch is defined as the rise of the roof above 12 inches. A 7/12 roof pitch, for example, signifies that the roof rises 7 inches for every 12 inches of horizontal height. A degree angle is commonly used outside of the United States.

Calculating different roofs and materials

The cost of the roof, as well as the roof area and the materials used, is determined by the roof pitch. It has an impact on both walkability and drainage, and roofs in places with a lot of rain or snow tend to have steeper pitches. The area of the roof is affected by the roof pitch. To estimate the actual size of the roof, a correction factor is required depending on whether the roof area is measured horizontally (perhaps from a design or image). Multiply the horizontal area by a correction factor related to pitch, as shown in the table below, given pitch and horizontal area measurement.

While it is feasible to estimate the quantity of materials required using simply the total roof area measurement, as shown in the table, the actual area of the roof can differ by up to 2.236 from the measured total area at a pitch of 24/12, depending on how large the pitch of the roof is. As a consequence, while measuring the size and pitch of each component of the roof and multiplying by the relevant correction factor might be time-consuming, it will provide the most accurate estimate of roofing materials required.

Slope Correction Factors

PitchAngleMultiply ByPitchAngleMultiply By


How do you calculate the roof area?

There are two ways to do that. One is to measure your roof and other way is to estimate roof measures.

What is your slope?

In order to determine this, measure the vertical rise of deck in inches over a 12 inch horizontal distance. If this rise is 4 inches, then your roof slope is 4 in 12.

What if you have a steep roof?

To calculate the roof length, you need to measure the exterior walls plus the overhang for the length parallel to the ridge. Next, throw some rope over the ridge and mark it on each eave. This will give you the width dimension to use in finding your area. This need to be done on each roof section which contains a horizontal ridge.

How about nails?

Generally, you need four nails per shingle.