How to Measure a Roof for Shingles (Without Climbing It)

Updated October 2, 2026

You can estimate a roof's area from the ground: measure the house footprint, add the overhang, and multiply by a factor for the roof's pitch. For a 30 × 40 ft house with a 6/12 roof, that's about 15 squares, or roughly 50 bundles of shingles with waste. The roofing calculator does this in one step.

Step 1: Measure the footprint

Measure the outside walls of the house with a long tape. Include an attached garage or porch if it's under the same roof. For an L-shaped house, split it into rectangles.

Step 2: Add the overhang

Eaves usually stick out 12–24 inches beyond the walls. Add twice the overhang to each dimension, because it's on both sides. A 30 × 40 ft house with 12 inch eaves becomes 32 × 42 ft, or 1,344 sq ft of "plan area".

Step 3: Find the pitch

Pitch is how many inches the roof rises for every 12 inches it runs horizontally. Three ways to find it without getting on the roof:

• In the attic: hold a level against the underside of a rafter, mark 12 inches along the level, and measure straight up to the rafter.
• From a ladder at the gable end: do the same against the roof edge (rake).
• With a phone app: many free inclinometer apps read the angle from a photo of the gable; convert the angle using the table below.

Step 4: Multiply by the pitch factor

For a single-pitch roof, this works the same for gable and hip roofs: the slope applies to the whole footprint. Hips and valleys add waste, not area.

Step 5: Convert to squares and bundles

squares = roof area × (1 + waste) ÷ 100
bundles = squares × 3 (for most shingles)

Use 10% waste for a simple gable roof, 15% for a hip roof, and up to 20% for roofs with dormers and several valleys.

Worked example

1. House 30 × 40 ft, 12 inch overhang: 32 × 42 = 1,344 sq ft plan area
2. 6/12 pitch: 1,344 × 1.118 = 1,503 sq ft of roof (15.0 squares)
3. Gable roof, 10% waste: 16.5 squares
4. × 3 bundles per square: 50 bundles

Don't forget the accessories

• Underlayment: synthetic rolls commonly cover 10 squares (1,000 sq ft).
• Ice and water shield: along eaves and in valleys in cold climates; measure in linear feet.
• Starter strip: the length of all eaves and rakes.
• Ridge cap: the length of all ridges and hips; a bundle typically covers 20–35 linear feet depending on the product.
• Drip edge: eaves plus rakes, sold in 10 ft lengths.

This ground estimate is great for budgeting. For a full re-roof, have a roofer or a satellite measurement report confirm the numbers before ordering, especially for complex roofs.