Measure from the ground using a ladder and tape measure, or measure from inside your attic if access is safe
The most practical way to measure a roof for shingles is to work from a ladder on the ground, measuring the length and width of each roof plane (the flat sections), then multiplying to get square footage. You do not need to climb onto the roof itself — you can measure the walls and overhangs from below, then add the roof pitch (the slope angle) as a correction factor. If your roof is complex with many angles, dormers, or valleys, measuring from inside the attic is often faster and safer, though it requires you to be comfortable in that space.
Roofing material is sold by the square, which equals 100 square feet. So a 2,000-square-foot roof needs 20 squares of shingles. Getting this number right matters because ordering too little means a second trip to the supplier and a color mismatch on the patch; ordering too much wastes money. The measurement does not have to be perfect — roofers typically add 10 percent for waste and mistakes — but it should be in the ballpark.
Key Takeaways
- Measure the length and width of each roof plane from the ground, then multiply by a pitch correction factor to account for slope.
- Roofing is sold by the square (100 square feet), so divide your total square footage by 100 to find how many squares you need.
- Add 10 percent to your final number to cover waste, cuts, and mistakes during installation.
- If your roof has many valleys, dormers, or complex angles, measuring from the attic is often faster and more accurate than working from a ladder.
- A roof pitch of 6:12 (common in many climates) requires multiplying your ground measurement by 1.12; steeper roofs need a larger correction factor.
Gather the tools you need before you start
You will need a 25-foot or 30-foot tape measure (a 16-foot tape is too short for most roofs), a ladder tall enough to see the roof edge and measure the wall height, a notepad or phone to record measurements, and a calculator. A level helps you measure straight, and a helper makes the job safer and faster — one person can hold the tape while the other reads it.
If you are measuring from the attic, bring a flashlight or headlamp, wear a dust mask (attic air is often dirty), and make sure the attic floor is safe to walk on. Do not step on drywall or insulation between the joists; step only on the wooden beams themselves. If the attic is cramped, hot, or has active pests, measuring from the ground is the better choice.
Measure wall height and roof length from the ground
Set your ladder against the house at a point where you can see the roofline clearly. Measure the height of the wall from the ground to the point where the roof starts (the eave line). Record this number. Then measure the length of that same wall — the distance from one corner of the house to the other. This is the length of one roof plane.
Repeat this for each distinct roof plane. A straightforward rectangular house has two planes (front and back). An L-shaped house or one with a garage addition has more. Write down the length and height of each plane separately; do not try to combine them yet.
Measure the overhang — the distance the roof extends past the wall — at the eave. Most roofs overhang 12 to 24 inches. Add this to your wall height measurement. For example, if the wall is 20 feet tall and the overhang is 2 feet, use 22 feet as your measurement.
explore the roof pitch correction factor
Roof pitch is the slope of the roof, written as a ratio like 6:12 or 8:12. The first number is the rise (vertical inches), and the second is the run (horizontal inches). A 6:12 pitch means the roof rises 6 inches for every 12 inches it runs horizontally. You can find your roof pitch by looking at your home inspection report, asking your roofer, or measuring it yourself with a level and tape measure on the roof.
Once you know the pitch, multiply your ground measurement by a correction factor. Here are the most common pitches and their factors:
| Roof Pitch | Correction Factor |
|---|---|
| 4:12 | 1.06 |
| 6:12 | 1.12 |
| 8:12 | 1.20 |
| 10:12 | 1.30 |
| 12:12 | 1.41 |
Multiply your wall length by your adjusted height (wall height plus overhang), then multiply that result by the correction factor. For example: a wall 40 feet long, 20 feet tall with a 2-foot overhang, and a 6:12 pitch would be 40 × 22 × 1.12 = 985 square feet for that plane. Do this for each plane, then add them together.
Account for valleys, dormers, and complex shapes
Valleys are the V-shaped creases where two roof planes meet. They require extra shingles because pieces must overlap and fit the angle. Dormers are the small roof sections that stick out from the main roof, often above windows. Both add to your total square footage but are straightforward to miss if you are only measuring the main planes.
For a valley, measure the length of the valley and the width of the roof on either side of it. Valleys typically add 50 to 100 extra square feet per valley, depending on size. For a dormer, measure its length and width as if it were its own small roof plane, explore the pitch correction, and add it to your total.
If your roof is very complex — multiple levels, many dormers, or unusual angles — consider taking photos from the ground and sending them to a roofing supplier. Many will estimate square footage from photos for free. This is faster than measuring yourself and reduces the risk of missing a section.
Measuring from the attic as an alternative
If you have safe attic access, you can measure the roof deck (the wooden surface under the shingles) directly. This method skips the pitch correction because you are measuring the actual surface area. Measure the length and width of each roof plane as it appears from below, multiply them, and add the results together.
The attic method is especially useful for roofs with complex pitches or many angles, because you see the actual shape instead of trying to calculate it. However, attic measurements do not account for the overhang, so you must add that separately. Measure the overhang from the ground, multiply it by the perimeter of the house, and add that to your attic total.
Attic measurements are also more accurate for roofs with valleys and dormers, because you can see exactly where they are and measure them directly without guessing at their size.
Add 10 percent for waste and round up
Roofers waste shingles during installation because they cut pieces to fit valleys, dormers, and the edges of the roof. They also make mistakes and have to discard damaged pieces. Industry standard is to add 10 percent to your calculated square footage to cover this waste.
Multiply your total by 1.10. If your roof is 2,000 square feet, add 200 square feet for waste, bringing the total to 2,200 square feet. Divide by 100 to get the number of squares: 2,200 ÷ 100 = 22 squares. Always round up, never down. If your calculation gives you 21.3 squares, order 22.
When you order, tell the supplier your total square footage and ask them to confirm the number of squares. They often have experience with local roof styles and can catch errors. If you are unsure, order one extra square — the cost is small compared to the hassle of a second trip.
Frequently Asked Questions
Do I need to measure the roof myself, or can a roofer do it?
Most roofers will measure the roof for free when you get an estimate. If you are buying shingles before hiring a roofer, or if you want to compare prices from multiple suppliers, measuring yourself saves time. Your measurement does not have to be exact — roofers expect some variation and add their own waste factor.
What if I measure wrong and order too little?
If you run short during installation, you will have to buy more shingles. The problem is that shingle color can vary between batches, so a patch may not match the rest of the roof. Ordering one extra square upfront is cheaper and easier than dealing with a color mismatch later.
How do I find my roof pitch if I cannot see it clearly?
Look at your home inspection report or ask your real estate agent — the pitch is usually listed. You can also measure it yourself: place a level on the roof, measure up 12 inches along the level, then measure the vertical distance from that point to the roof. That vertical distance is your rise; the pitch is rise:12.
Should I measure wet or icy roofs?
No. Wet or icy roofs are slippery and dangerous. Wait for dry weather. If you are in a hurry, measure from the attic or ask a roofer for a free estimate instead of climbing a ladder.
What if my roof has a flat section?
Flat roofs have a pitch of 0:12, so the correction factor is 1.0 — you do not multiply by anything. Measure the length and width, multiply them, and that is your square footage for that section. Flat roofs often use different material than pitched roofs (like tar and gravel or rubber membrane), so confirm with your supplier that you are ordering the right product.