A complete step-by-step guide to measuring your roof accurately, calculating pitch, and estimating the materials you need for your shingle replacement project.
Measuring your roof for shingles is the first and most important step in planning a roof replacement. An accurate measurement helps you buy the right amount of materials, avoid costly shortages, and compare contractor quotes more confidently.
Start by sketching your roof from a bird's-eye view. Break the roof into simple rectangles, with each roof plane as its own section. A basic gable roof has two rectangles, while a hip roof has four or more.
Label each section with a letter and write down the length and width of each one as you measure. This makes it easier to double-check your work and avoid missing a section.
Use a tape measure that is at least 25 feet long. Measure the length and width of each roof plane. For safety, use exterior wall measurements from the ground when possible, or measure from inside the attic.
Safety warning: Never walk on a wet, icy, or steep roof. If you are not comfortable working at height, measure from the attic or ask a professional to help.
Roof pitch describes how steep your roof is. It matters because the actual sloped area is larger than the building footprint.
To measure pitch from the attic, hold a level against a rafter, measure 12 inches horizontally, and then measure the vertical rise at that point. If the rise is 6 inches, the pitch is 6/12.
| Pitch | Angle | Multiplier | Common Use |
|---|---|---|---|
| 4/12 | 18.4 deg | 1.054 | Low-pitch homes |
| 6/12 | 26.6 deg | 1.118 | Standard residential |
| 8/12 | 33.7 deg | 1.202 | Steeper traditional roofs |
| 10/12 | 39.8 deg | 1.302 | Very steep roofs |
| 12/12 | 45 deg | 1.414 | 45-degree roof angle |
To estimate actual roof area, multiply the footprint area by the pitch multiplier. For example, a 1,200 sq ft footprint with a 6/12 pitch becomes about 1,342 sq ft of roof area.
Roofing materials are sold by the square. One roofing square equals 100 square feet.
If your roof area is 1,342 sq ft, divide by 100 to get 13.42 squares. You should round up, so you would order 14 squares before waste.
You always need extra material for cuts, trimming, and fitting around valleys, ridges, and penetrations.
Using the example above, 13.42 squares with 10% waste becomes 14.76 squares, which rounds up to 15 squares.
Beyond shingles, most roof jobs also need underlayment, drip edge, ridge vents, nails, and starter shingles.
Instead of doing the math by hand, use our roofing calculator. It helps you estimate roof area, material quantities, and cost in a few minutes.
Measuring individual planes is more accurate, especially for complex roofs. Footprint-based estimates work best on simple rectangular homes.
Most standard asphalt shingles are sold three bundles per square, though this varies by product type and manufacturer.
Satellite tools can help with rough dimensions, but they do not account for pitch accurately. They work best as a cross-check, not your only measurement method.
For simple roofs, DIY measuring is usually fine. For steep or complex roofs, a professional measurement can reduce mistakes and help avoid ordering the wrong amount of material.