Start with your roof's total square footage

The first step is to measure or find the total area of your roof in square feet. If you have the original blueprints or a recent appraisal, the roof area may already be listed. If not, you can calculate it by measuring the length and width of each roof plane (the sloped sections), then multiplying length by width. A roof with a steep pitch covers more area than a flat roof of the same footprint, so measure the actual sloped surface, not just the ground below it.

If your roof has multiple sections at different angles or heights, measure each plane separately and add them together. For a straightforward rectangular roof, this is straightforward. For complex roofs with valleys, dormers, or multiple peaks, break it into smaller rectangles and triangles, measure each, and sum the totals.

Once you have the total square footage, divide by 100. Roofing material is sold in units called "squares," and one square equals 100 square feet. So a 2,000-square-foot roof requires 20 squares of shingles.

Key Takeaways

  • One roofing square equals 100 square feet, so divide your total roof area by 100 to find how many squares you need.
  • Measure the actual sloped surface of your roof, not the ground footprint, because pitch affects the total area.
  • Add 10 percent to your square count to account for waste, cuts, and mistakes during installation.
  • Shingles are bundled in groups that cover a fraction of a square, so check the bundle coverage before you buy.
  • If your roof has a steep pitch or complex layout, consider hiring a roofer to measure rather than doing it yourself from a ladder.

Account for waste and overlap

Roofers do not use every shingle they buy. Shingles are cut at edges, around vents and chimneys, and at valleys where two roof planes meet. Some are damaged during handling or installation. Industry standard is to add 10 percent to your calculated square count to cover this waste.

So if your roof is 20 squares, order 22 squares of shingles. This buffer also protects you if you miscalculated the roof area slightly or if the shingles you chose are discontinued before you finish and need to buy more to match.

Understand how shingles are bundled and sold

Shingles are not sold by the square. They are bundled in packages, and the number of bundles per square varies by shingle type and weight. A standard asphalt shingle bundle typically covers about 33 square feet, so you need roughly three bundles to cover one square. Heavier architectural or dimensional shingles may only cover 25 to 30 square feet per bundle, requiring four or more bundles per square.

Check the coverage listed on the bundle label before you buy. The label will say something like "covers 33.3 sq. ft." or "3 bundles per square." Multiply the number of squares you need by the bundles per square for your chosen shingle type to get the total number of bundles to order.

If you calculated 22 squares and your shingles require three bundles per square, you need 66 bundles. If they require four bundles per square, you need 88 bundles. The difference is significant, so do not assume all shingles bundle the same way.

Measure roof pitch if you cannot access the roof

If you cannot safely climb onto your roof, you can estimate pitch from the ground. Pitch is expressed as a ratio — for example, 6:12 means the roof rises 6 inches for every 12 inches of horizontal distance. A steeper pitch means more surface area and more shingles needed.

To measure pitch without climbing, use a level and a tape measure. Hold the level horizontally against the roof edge as viewed from the ground or a ladder. Measure up from the end of the level to the roof surface. If the roof rises 6 inches over a 12-inch level, your pitch is 6:12. Once you know the pitch, you can use an online roof area calculator or a roofer's pitch multiplier table to convert your ground footprint into actual roof area.

Alternatively, ask a roofer for a free measurement. Many will measure your roof at no cost if you are getting estimates for the work.

Account for roof features that reduce shingle coverage

Vents, chimneys, skylights, and other penetrations reduce the area you actually need to cover with shingles. For a typical residential roof, subtract about 10 square feet for each vent or small penetration and 50 to 100 square feet for a chimney or large skylight.

Do not subtract these areas from your total before calculating waste. Instead, calculate your shingle order based on the full roof area minus penetrations, then add the 10 percent waste buffer on top. This ensures you have enough material even after accounting for the features that interrupt the shingle field.

Use a roof measurement tool or hire a professional

If you are uncomfortable measuring from a ladder or your roof is very steep or complex, several alternatives exist. Some roofing suppliers offer free measurement services when you purchase from them. You can also use satellite imagery tools — Google Earth and some roofing calculators let you outline your roof on a map and estimate the area, though this method is less accurate than a physical measurement.

A professional roofer will measure your roof as part of a free estimate. If you are planning to hire someone to install the shingles anyway, let them do the measuring. If you are doing the work yourself, the cost of a professional measurement is usually worth the accuracy, especially on larger or more complex roofs.

Double-check your math before ordering

Write down each step: total roof area in square feet, divided by 100 to get squares, plus 10 percent for waste, then multiplied by the bundles per square for your chosen shingle type. Check your arithmetic twice. A calculation error can mean ordering too few bundles and running short mid-project, or too many and wasting money.

If you are unsure about your measurements or calculations, contact the roofing supplier with your roof dimensions and pitch. Many will calculate the shingle count for you based on the information you provide. This is a free service and takes the guesswork out of the order.

Frequently Asked Questions

What if I measure my roof and get a number that does not divide evenly by 100?

Round up to the next whole square. If your roof is 1,850 square feet, that is 18.5 squares, which rounds to 19 squares. Then add 10 percent for waste (19 × 1.10 = 20.9, round to 21 squares). Always round up, never down, so you do not run short.

Do I need to measure the underside of roof overhangs?

Yes, if the overhang is covered with shingles. Measure the full sloped surface from the edge of the overhang to the peak. If the overhang is only soffit and fascia (not shingles), do not include it in your roof area calculation.

How do I measure a roof with multiple levels or a complex shape?

Break it into straightforward shapes — rectangles and triangles. Measure each section separately, calculate the area of each, then add them together. For triangular sections, use the formula (base × height) ÷ 2. If this feels too complicated, hire a roofer to measure.

Can I use my roof's square footage from my property tax assessment?

Not reliably. Tax assessments usually list the ground footprint or the interior square footage of the house, not the actual roof surface area. Always measure the roof itself or have a roofer do it.

What if I buy too many shingles?

Most suppliers will accept returns of unopened bundles within a set timeframe, usually 30 days. Keep your receipt and the original packaging. If shingles are discontinued, you may not be able to return them, so it is better to order slightly too few and buy a small amount extra later than to over-order significantly.