How do you calculate square footage for a metal roof?

Figuring out the square footage for a metal roof installation is an important step in determining the materials and costs for your roofing project. By accurately calculating the total square footage, you can get an accurate estimate of how much metal roofing you will need to purchase. Here are some tips on how to properly measure and calculate the square footage of your roof.

What Tools Do You Need to Measure?

To measure your roof accurately, you will need the following tools:

  • Measuring tape – Use a long, retractable measuring tape that is at least 25 feet long. This allows you to measure long distances without having to move the tape multiple times.
  • Ladder – Use an extension ladder or multi-position ladder to safely access all areas of the roof for measuring.
  • Satellite imagery – Online satellite imagery or aerial photos of your property can help you identify the size and shape of your roof before climbing up to measure.
  • Estimating calculator – There are various roofing calculators online that can help estimate square footage based on roof dimensions.
  • Graph paper – Mapping out the shape of your roof on graph paper first can make it easier to calculate when on the roof.

Make sure to use appropriate safety equipment like a harness when working on the roof. It is also recommended to get an assistant who can help provide measurements from the ground.

How to Measure Your Roof

When you are up on the roof and ready to start measuring, follow these steps:

  1. Measure the full length and width of the roof to get its overall dimensions. Include any overhangs in your measurements.
  2. Divide the roof into smaller sections if it has multiple ridges or changes in direction. Measure each section individually.
  3. For sloped roofs, measure horizontally along the edges, not diagonally up the slope. This will give you the true length and width.
  4. For dormers, chimneys, skylights and other projections, take separate measurements of their dimensions.
  5. For eaves, measure the overhang separately from the main roof dimensions.
  6. Write down all measurements as you go, rounding to the nearest foot. Draw a simple sketch of the roof with all dimensions marked.

Taking methodical measurements is key for getting accurate square footage totals. Don’t rely on estimating or guessing – measure every part of the roof carefully from edges to ridges to protrusions.

Calculating Total Square Footage

Once you have all the measurements, you can use the following formula to calculate the total square footage:

Total Roof Square Footage = Length x Width of Each Section

So for example, if you have a simple rectangular roof:

  • Length: 40 feet
  • Width: 30 feet

The math would be:

40 x 30 = 1,200 square feet

For a roof with multiple sections, calculate each section separately then add them together for the total.

Let’s say you also measured a dormer that was 10 feet long by 5 feet wide. The math for that section would be:

10 x 5 = 50 square feet

So the total for the entire roof is:

Main roof: 1,200 square feet
Dormer: 50 square feet
Total: 1,250 square feet

Make sure to account for all sections and protrusions in your final square footage calculation.

Using an Estimating Calculator

There are also various metal roofing calculators online that can help estimate the square footage of your roof using the measurements you provide.

Simply enter the length, width and pitch of each roof section into the calculator. It will provide you with the total estimated square footage amount. This can serve as a good double check of your manual calculations.

Some things to keep in mind when using an estimating calculator:

  • Make sure your measurements are accurate before inputting them.
  • Remember to include overhangs in your length/width measurements.
  • Enter a pitch percentage if required – use a level to check this.
  • Account for all ridges, valleys, dormers and protrusions.
  • Round measurements to the nearest foot before inputting.

Using a metal roofing calculator along with taking meticulous measurements is the best way to get an accurate roof square footage estimate.

Why Proper Square Footage is Important

Getting the right square footage amount for your roof is important for several reasons:

  • Ordering materials – Knowing the square footage will tell you exactly how much metal roofing and other supplies you need to order.
  • Cost estimates – Metal roofing costs are typically quoted per square foot. Accurate footage allows contractors to provide precise quotes.
  • Installation time – The installation timeframe and labor costs are also dependent on having the correct square footage.
  • Minimizing waste – Overestimating square footage can cause you to order excess materials that go to waste. Accurate calculations reduce unnecessary costs.

In summary, properly measuring and calculating the square footage of your roof takes some time and effort, but is well worth it for getting accurate quotes and ensuring you purchase the right amount of materials for your project.

Tips for Accurate Measurements

Here are some helpful tips to keep in mind for taking accurate roof measurements:

  • Use a high-quality measuring tape – Avoid stretchy cloth tape measures which can give incorrect lengths.
  • Always measure from edge to edge – Don’t estimate or shortcut measurements.
  • Have two people measure – One person on the roof and one on the ground to confirm.
  • Take pictures of each section after measuring.
  • Write down all measurements immediately – Don’t rely on memory.
  • Map out roof on graph paper prior to measuring.
  • Walk around perimeter before climbing up to observe overall shape and size.
  • Break roof into smaller sections for easier measuring.
  • Double check all calculations.

Taking the time to be extremely precise with your measurements will pay off in the long run with a properly installed metal roof.

Common Mistakes to Avoid

It’s easy to make mistakes when calculating square footage for the first time. Here are some common errors to avoid:

  • Only multiplying length x width once – Make sure to calculate every roof section separately.
  • Forgetting to account for protrusions like dormers and chimneys.
  • Measuring diagonally up sloped roofs instead of horizontally.
  • Not including overhangs in length and width measurements.
  • Using a cloth tape measure that stretches over long distances.
  • Rounding measurements too soon – only round at the very end.
  • Transposing numbers when writing down measurements.
  • Forgetting to double check all calculations.

Being aware of these common mistakes can help you avoid making errors in your final square footage amount.

When to Hire a Professional

For DIY homeowners taking on their own metal roofing project, carefully measuring and calculating square footage is part of the process. However, for larger or more complex roofing jobs, it may be advisable to have a professional roofing contractor or estimator take measurements and determine the square footage for you.

Here are some signs it may be better to get professional assistance with your measurements:

  • Roof has multiple layers or modifications from original construction.
  • Roof has complex geometry with lots of pitches, valleys and ridges.
  • Standing seam metal roofing is being installed (requires precision).
  • You don’t feel fully comfortable taking measurements safely.
  • Existing home plans or roof structure drawings are unavailable.
  • Rooftop obstructions like solar panels make measuring difficult.

Hiring a skilled roofing contractor to measure your roof costs a little more upfront but can give you peace of mind that the square footage calculation is perfect. They have the right equipment and experience measuring all types of roofs.


Finding the square footage of a metal roof requires carefully measuring all sections of the roof and using the length x width formula to calculate totals. Being extremely precise with your measurements, using tools like satellite imagery and calculators, and avoiding common mistakes will ensure you get an accurate result.

With the right square footage amount, you can confidently estimate how much metal roofing material is required, get accurate cost quotes, minimize waste, and end up with a beautifully installed metal roof. For larger or complex roofs, don’t hesitate to bring in a roofing professional to handle the measurements.

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