Roofing Calculator
Enter the building size, roof pitch and overhang. You get roof area, roofing squares and how many bundles of shingles to buy. Results update as you type.
Roof area
1,409 sq ft
14.1 squares · 15.5 with 10% extra · 130.9 m²
About 47 bundles of shingles for 15.5 squares, with 10% extra.
- Pitch multiplier1.118
- Squares (100 sq ft each)14.09
- Squares with extra15.50
- Shingle bundles (3 per square)47
- Underlayment rolls (10 squares)2
- At your price per squareAdd a price
- Shingles at your price per bundleAdd a price
Simple model: one pitch on every plane and the same overhang on all sides. Valleys, dormers, chimneys and a steep or cut-up roof need more extra.
Planning estimate, not a quote. Disclaimer
How the roofing calculator works
A sloped roof is bigger than the footprint underneath it. The calculator adds your overhang to the building size, then multiplies by the pitch multiplier, which is the sloped length for every foot of run. Squares are the area divided by 100, because roofers price and sell in 100-square-foot squares. Shingle bundles come from the squares: three bundles cover a square for most asphalt shingles.
Multiplier = √(12² + rise²) ÷ 12
Roof area = footprint × multiplier
Squares = roof area ÷ 100
Bundles = squares × (1 + extra %) × 3, rounded up
Example: A 40 × 28 ft house with 12-inch overhangs and a 6/12 roof: footprint with overhang 42 × 30 = 1,260 sq ft, × 1.118 = 1,409 sq ft of roof, or 14.1 squares. With 10% extra that is 15.5 squares and 47 bundles.
Pick the pitch you have
The pitch is the rise in inches for every 12 inches of run, written as 6/12 or 6:12. Not sure of yours? Use the roof pitch calculator, or read it from the pitch chart. Every common pitch has a page with its angle, multiplier and area:
What else you can work out
- Shingle calculator: bundles of field shingles, starter strip and ridge cap.
- Roof square calculator: square footage and squares, from a footprint or a known area.
- Underlayment calculator: rolls of synthetic underlayment and ice-and-water barrier.
- Metal roof calculator: number of panels and the length of each.
- Rise over run calculator: slope, run, rise and diagonal from any two, in pitch, percent, ratio or degrees.
- Rafter length calculator: common rafter length, cut length and count.
- Roof truss calculator: truss height, chord lengths and web member lengths, with a diagram.
- Roof cost calculator: an estimate that uses only prices you type in.
Tips before you order
- Measure the walls, not the roof. Add dormers, porches and garages as separate runs and add the areas.
- GAF suggests adding 10 to 15% for trim and waste. The calculator uses 10% by default; use more for hips, valleys and cut-up roofs.
- Round up. Shingle bundles from different lots can vary in color, so order all you need at once.
- Get a roofer's measurement for the final order. This is a planning estimate.
Frequently asked questions
How do I calculate roof area from the footprint?
Multiply the footprint (including the overhang) by the pitch multiplier. For a 6/12 roof the multiplier is 1.118, so a 1,000 sq ft footprint is about 1,118 sq ft of roof.
How many squares are in a roof?
One roofing square is 100 sq ft of roof surface. The example roof above is 1,409 sq ft, which is 14.1 squares.
How many bundles of shingles do I need?
Most asphalt shingles come three bundles to the square. The example roof needs 15.5 squares with 10% extra, which is 47 bundles.
How much extra should I add for waste?
GAF suggests 10 to 15% for trim and waste. Use the higher end for hip roofs, valleys, dormers and roofs with many small planes.
Does the roofing calculator work in metric?
Yes. Switch to meters and centimeters to get area in square meters. Squares and bundles are still based on the US 100-square-foot square.
Can I get a price from this calculator?
Only from prices you enter. The site holds no regional price data. Add your price per square or per bundle, or use the roof cost calculator.
Related
Other roofing calculators
Sources
- GAF: How many bundles of shingles are in a square? (checked Nov 12, 2026)
- GAF: Minimum slope for shingles (checked Nov 12, 2026)