MaterialScopeHow to measure a roof for shingles
Find roof square footage and edge lengths from the ground, using the footprint, the pitch and a few simple multiplications.
Stay on the ground
You do not need to walk the roof to estimate materials. Measure the outside walls with a tape measure, add the overhang on each side, and find the pitch from the attic or the gable end. Use house plans if you have them. Climbing a roof without proper fall protection is dangerous; leave on-roof measuring to a roofer.
Step 1: measure the footprint
Measure the length and width of the house, then add the overhang at each edge. A 38 × 28-foot house with 1-foot overhangs all around has a 40 × 30-foot roof footprint. Split L-shaped or T-shaped houses into rectangles and measure each one separately.
Step 2: find the pitch
Pitch is the rise in inches for every 12 inches of horizontal run. Hold a level horizontally against a rafter in the attic or the underside of a rake board, mark 12 inches along the level, and measure straight up to the rafter. A 6-inch measurement means a 6:12 pitch. The roof pitch calculator converts any rise and run into a pitch, an angle and a multiplier.
| Pitch | Multiplier | 40 × 30 ft footprint becomes |
|---|---|---|
| 4:12 | 1.054 | 1,264.91 ft² |
| 6:12 | 1.118 | 1,341.64 ft² |
| 8:12 | 1.202 | 1,442.22 ft² |
| 10:12 | 1.302 | 1,562.05 ft² |
| 12:12 | 1.414 | 1,697.06 ft² |
Step 3: multiply
Footprint × multiplier gives roof surface area. This works for gable and hip roofs alike, provided every plane has the same pitch: the slope stretches the whole footprint by the same factor. If different sections have different pitches, calculate each section separately and add them. Add dormers and other projections as their own sections.
Step 4: measure the edges
Edge lengths drive starter strip, drip edge and ridge cap. Eaves are the level bottom edges. Rakes are the sloped edges at the gable ends; each one is half the footprint width × the multiplier. Ridges and hips are the peaks where planes meet.
| 40 × 30 ft footprint, 6:12 | Gable roof | Hip roof |
|---|---|---|
| Roof surface | 1,341.64 ft² | 1,341.64 ft² |
| Eaves | 80 ft (2 × 40) | 140 ft (full perimeter) |
| Rakes | 67.08 ft (4 × 16.77) | none |
| Ridge + hips | 40 ft ridge | 10 ft ridge + 4 × 22.5 ft hips = 100 ft |
The hip lengths come from geometry: each hip runs diagonally over 15 ft × √2 = 21.21 ft of plan distance while rising 7.5 ft, so its length is √(21.21² + 7.5²) = 22.5 ft. The ridge is the footprint length minus its width: 40 − 30 = 10 ft.
Step 5: turn measurements into materials
Enter the footprint, pitch and edge lengths in the roofing calculator. For the gable example with 10% extra, it gives 45 shingle bundles, 2 bundles of starter, 17 pieces of drip edge, 2 bundles of ridge cap and 2 rolls of underlayment. For the hip version, enter 140 ft of eaves, 0 rakes and 100 ft of ridge and hips; the ridge cap rises to 5 bundles. Product coverages vary, so check each label.
Check before you order
Compare your area with a roofer’s measurement or an aerial report if you get one; a difference of a few percent is normal. Valleys, skylights, chimneys and complex cut-up roofs can raise waste above 10%. Ask your installer what allowance suits the roof.
Product reference: Owens Corning roofing product documents. Confirm the current label for your chosen product.
Change the measurements and allowance to match your plan.
Open Roofing CalculatorMaterialScope editorial · Updated October 21, 2026 · Calculation methodology