Roofing Area and Shingle Calculator

Photo: Vipada / Adobe Stock

This roofing calculator will help you calculate shingles for your project and find the total number you’ll need to cover your roof, including an overage of about 10%. It also covers how many squares you’ll need and how many bundles of shingles you’ll want to buy for your project. Use the calculator to automate most of the math, and follow the steps below to order the correct amount of materials. Once you have the final numbers, you can estimate your shingle installation costs.

In this article:

1. How to Calculate Roof Size and Materials
1. Step 1: Calculating Roof Area
2. Step 2: Convert to Squares
3. Step 3: Determine the Amount of Shingles Needed
4. Step 4: Determine Overage and Waste
2. Other Roofing Materials

How to Calculate Roof Size and Materials

If you don’t want to use the roof square footage calculator above, use the following steps to manually calculate how many shingles you’ll need for your project. We also recommend adding an extra 10% to account for overage or waste, which always happens when shingles overlap on the edges and valleys of the roof. Your final cost will depend on the type of shingle, but asphalt and composition roof shingles cost $30 to $50 per bundle or $1 to $1.50 per square foot.

Step 1: Calculating Roof Area

If you choose not to use the roof area calculator above, you’ll need to do a few manual steps to adjust for the slope of the roof. First, calculate the area of the roof by multiplying the length times the width, as if you were standing on a flat roof. Multiply the length times the width. Make sure to use measurements going all the way to the roof’s edge, including the eaves. Do not use the area of your home for this.

If you need to, break up your roof into multiple square or rectangular sections to find the base area, multiply by the slope of that area, and add the numbers together. You can use the roof area calculator or any basic area calculator to help determine this.

Follow these steps:

1. Measure the first section’s length and width.
2. Multiply these two together to get the base area.
3. Multiply the base area by the multiplier that aligns with the roof’s slope in the chart below to find the actual area. Find the pitch in column one, and then use the corresponding multiplier from column three. The resulting number is the actual square footage of your roof.
4. Repeat the previous steps for each square or rectangular section.
5. Add all of these numbers together to find the actual area of the roof.
6. Use this final number in the next section to determine the number of squares.

*Do not use shingles on pitches of 2/12 or lower. Use rolled roofing or metal roofing for low and flat roofs.

Step 2: Convert to Squares

Roofing contractors work in squares, not square feet. This roofing square calculator step converts square feet to squares.

1. To find the number of squares needed, divide the result from the last step by 100 and round up to the nearest square.

Step 3: Determine the Amount of Shingles Needed

SIngles typically come in bundles that cover about 33 square feet of space, so three bundles usually cover 100 square feet or one square.

1. Divide the number of squares by three, assuming the shingles come in a standard bundle with roughly 32 to 33 square feet of coverage.

A few non-standard bundles have less than 33 square feet of shingles. This depends on the type of shingles you’re working with, but it typically applies to thick, high-end shingles. To find how many bundles of shingles are in a square, simply divide 100 by the square foot coverage noted on the bundle.

Step 4: Determine Overage and Waste

As mentioned above, most contractors account for about 10% of waste. This comes from shingles being cut to fit in valleys and along eaves, since they are laid offset to adjacent rows. Typically, you’ll need about two to three extra squares to cover waste. Here are two different ways to calculate the overage.

• Method 1:Multiple the total area of your roof by 10%.
• For example, for a 3,000-square-foot roof, you would calculate 3,000 x 10% = 300. So you would estimate the need for 3,300 square feet of total coverage.
• Method 2:Take the number of bundles of shingles you need and multiply by 10%.
• For example, a 3,000-square-foot roof requires 30 squares, which means you’ll need 90 bundles of shingles. Multiply 90 x 10% = 9. (Nine bundles at 33 square feet each means 297 square feet of coverage).

You can then use this final number to figure out your total roof replacement cost, or more specifically, asphalt shingle roof costs or composite shingle costs. You’ll spend varying amounts depending on the type and quality of the shingle you need.

Other Roofing Materials

You’ll need a few other materials for the job. At a minimum, you’ll need:

• Roof underlayment:Purchase enough square footage to cover your entire roof plus at least 10%. You’ll overlap each row by about 2 inches.
• Roofing nails: You’ll need 320 roofing nails per square. So, take the number of squares you need and multiply by 320.
• To get specific, use the single calculator equation of 29 shingles per bundle with four nails per shingle (5 nails per starter shingles).
• Vent ridge caps: Simply measure the ridge of each section of roof and add the numbers together. You’ll need this many ridge caps. Most shingle manufacturers make matching vents for their shingles.

Your local roofer will include these extra roofing materials in your estimate.

11 Comments

1. William McKleroy, July 7:

   I am roofing the house trailer and need to know how many packs of shingles needed,

2. Cecil Venturella, March 3:

   1square of roofing covers 100 square feet of roof a bundle is 1/3 of a square. Get the square footage of roof and divide it by 100 and it will give the number of squares you need and for every decimal number over 3 buy a bundle to achieve the amount of material. Hope it helps

3. Alan J Warshawer, August 13:

   This in not applicable to a flat roof

4. Jerrold Simpson, August 31:

   You should not put shingles on a flat roof. If you are going to use shingles, build a pitched roof over the mobile home. The dead air space between the metal roof and shingle roof will work as a barrier to dissipate heat.
   You should use rolled roofing on a flat roof, over lap 1/2 the width of the rolled roofing.
   A mobile home roof should not be flat. It should have a curved roof. Rolled roofing is best on a mobile home anyway.

5. richard laham, September 5:

   what about peaks and valleys? Is there a standard allowance for scrap?

6. Tee, September 10:

   im wanting to do a metal roof on my 16 x 80 mobile home. How much metal tin will I need as well as the thickness? Thanks in advance.

7. Alesia, October 7:

   According to your calculator my “Actual Square Feet of House” is 4807.5 &
   “Numbers of Squares Needed” is 53.
   The numbers I used are based on the proposal from my roofer: 3698 sq ft with predominant 10/12 pitch.
   The problem is my roofer is saying only 41 squares are needed. Can you help me reconcile the difference?

8. Shana Dockery, October 30:

   How much metal would I need to put on a 76inch foot long by 28 inch wide mobile home roof

9. ZsaZsa, March 21:

   My roofer told me my roof is 13 square, how many bundles of shingles will I need? How would I calculate for the underlayment (tar paper & weather barrier)? My house is a 24 x 60 modular home including the porch roof.

10. bo williams, June 16:

    My home is 5100 sq ft. Total. How many squares are on the roof? I was taught to always go 5 squares over the footprint. Is this true?

11. Sam ellis, June 18:

    How much material will it take to put a roof on a house 2800sq ft