Measure from the ground using a ladder and tape measure

The most straightforward way to measure a roof is to climb a ladder, measure the length and width of each roof plane, and multiply them together. You will need a tape measure (at least 25 feet), a ladder that reaches your eaves safely, and a notebook to record dimensions. Start at one corner of the roof and measure the length along the eave, then measure the width from the eave to the peak or ridge. For a straightforward rectangular roof, one length and one width give you the total square footage. For roofs with multiple sections or angles, measure each plane separately and add them together.

Safety matters more than speed. Wear shoes with good grip, have someone hold the ladder base, and never lean sideways — move the ladder instead. If your roof is steep, wet, or higher than one story, consider hiring a professional measurer rather than climbing yourself. A fall from a roof causes serious injury.

Key Takeaways

  • Roof area is measured in square feet by multiplying the length and width of each roof plane, then adding all planes together.
  • A tape measure, ladder, and notebook are the only tools you need for a basic measurement from the ground.
  • Steep roofs, high roofs, and roofs with complex angles are safer to measure by hiring a professional or using aerial photography.
  • Roofers and material suppliers often measure roofs themselves before giving you a quote, so your measurement does not have to be perfect.
  • Roof pitch (the angle of the slope) affects how much material you need, so note whether your roof is flat, gently sloped, or steep.

Account for roof pitch when calculating material needs

The pitch of your roof — how steep it is — changes how much material you actually need. A flat roof's square footage is the same as the footprint of your house. A pitched roof covers more area because the slope adds length. If your roof is pitched, you cannot straightforward measure the ground footprint and call it done.

To account for pitch, measure the actual roof surface itself, not the ground below it. Climb the ladder and measure from the eave straight up the slope to the peak or ridge. This sloped measurement is longer than the horizontal distance would be. Multiply this sloped length by the width of that roof plane. Do this for each sloped section. Roofers call the result the "true roof area," and it is what you need to order shingles, metal panels, or other roofing material.

If you do not want to climb, you can estimate pitch by measuring the vertical rise and horizontal run. Measure up 12 inches vertically from a point on the roof, then measure horizontally from that point until you reach the same height as the roof surface. If that horizontal distance is 4 inches, your pitch is 12:4, or 3:1. Steeper pitches mean more material per square foot of ground area.

Use aerial photography or satellite images as an alternative

Google Earth, Bing Maps, and similar services show your roof from above. You can measure distances on these images using the built-in ruler tool. Open the image of your property, use the measurement feature to mark the length and width of each roof plane, and the tool will calculate square footage for you. This method works well for straightforward roofs and keeps you off the ladder.

The limitation is that aerial images do not show pitch. A satellite photo shows the footprint of your roof, not the actual sloped surface area. For a flat roof, the aerial measurement is accurate. For a pitched roof, you still need to account for slope separately, or hire someone to measure the actual surface. Aerial measurement is a good starting point, but confirm the pitch before ordering materials.

Hire a professional if the roof is complex or unsafe

Roofers, home inspectors, and roofing material suppliers often measure roofs as part of their service. A professional brings a ladder, knows how to move safely on a slope, and can spot problems while measuring — missing shingles, soft spots, or water damage that affects what needs to be replaced. Many will measure for free if you are getting a quote from them anyway.

Professional measurers also use tools like laser measures and drones for steep or complex roofs. A drone photograph gives a clear view of the entire roof surface and can be measured afterward without anyone climbing. This costs more than a ground measurement but is worth it for multi-story homes, roofs with many angles, or situations where climbing is risky.

Record your measurements in a way you can use later

Write down the length and width of each roof plane, the pitch, and the total square footage. Take a photo of your notes and of the roof itself so you have a record. If you are getting quotes from roofers, send them your measurements and photos — they may verify them on-site, but having your numbers in writing speeds up the process.

When you order materials or get a roofing estimate, the supplier or contractor will often re-measure to confirm. This is normal and does not mean your measurement was wrong; they are protecting themselves against mistakes. Your measurement is useful for your own planning and for comparing quotes, but the final order usually goes by the professional's measurement.

Understand how square footage translates to material and cost

Roofing material is priced and sold by the square, which equals 100 square feet. A 2,000-square-foot roof needs 20 squares of shingles. Suppliers and roofers use this unit because it is how bundles are packaged and how labor is quoted. Knowing your roof's square footage lets you estimate material cost and compare prices between suppliers.

The actual amount of material you order is usually 10 to 15 percent more than the calculated square footage. This accounts for waste from cutting, overlaps at seams, and mistakes. A roofer will add this waste factor automatically when they quote you. If you are buying material yourself, ask the supplier how much extra to order for your roof pitch and complexity.

Frequently Asked Questions

Do I need to measure my roof myself, or can I just tell a roofer to measure it?

You can ask a roofer to measure, and most will do it as part of giving you a quote. Measuring yourself first is useful if you want to compare quotes from multiple roofers or if you are planning a project and want to know the scope before calling anyone. Either way, the roofer will likely re-measure on-site.

What if my roof has a very steep pitch or is three stories high?

Do not climb a steep or high roof yourself. Hire a professional roofer or home inspector to measure, or ask a roofing company to send someone out. Many will measure for free if you are getting an estimate from them. A drone measurement is also an option for complex roofs.

How accurate does my measurement need to be?

For ordering materials, within 5 to 10 percent is acceptable because roofers add waste anyway. For budgeting or comparing quotes, a rough measurement is enough to get in the ballpark. If you are off by a few square feet on a 2,000-square-foot roof, it will not change the price significantly.

Can I measure my roof from inside my attic?

You can measure the attic floor to get the footprint, but you still need to account for pitch to know the actual roof surface area. Measuring from the attic does not tell you the slope. Climb to the roof surface itself or use an aerial image plus a pitch measurement.

What if I cannot find the peak or ridge of my roof?

If your roof is flat or nearly flat, measure from one eave to the opposite eave in both directions. If your roof has a ridge you cannot see from the ground, climb the ladder and look for it, or ask a roofer to point it out during a quote. Some roofs have multiple ridges if they have valleys or complex angles — measure each section separately.