Roofing Calculator

Work out your roof's area from the size of the house and the roof pitch, how many roofing squares that is, and how many bundles of shingles to buy with an allowance for waste. Your inputs stay in your browser.

Your roof and shingles

The roof

Measured on the ground, including the overhang at each end.

Including the overhang on each side.

Inches of rise per 12 inches of run; 4 to 8 is common. Enter 0 for a flat roof.

The shingles

About 10% for a simple gable roof, 15% for a hip roof or dormers, more for complex roofs.

Printed on the wrapper: usually 3, sometimes 4 for heavier shingles. A square is 100 sq ft.

45 bundles for 13.42 squares of roof. See full results

Example: a 40 × 30 ft footprint including overhangs, a 6/12 pitch, 10% extra and 3 bundles per square. Enter your numbers to update.

Your roofing estimate

Bundles to buy
45
At 3 bundles per square
Roof area
1341.6 sq ft
13.42 squares; 14.76 squares with 10% extra

From footprint to bundles

StepValue
Footprint (40 × 30 ft) 1200.0 sq ft
Pitch factor for 6 in 12 1.1180
Roof area 1341.6 sq ft
With 10% extra 14.76 squares
Bundles, rounded up 45

Add a price per bundle to estimate the cost.

Ridge caps, starter strip, underlayment, flashing and nails are sold separately.

How to calculate roofing

  1. Footprint: measure the house on the ground, adding the overhang on every side: 40 × 30 = 1,200 square feet. If you measure in inches, divide square inches by 144 for square feet (NIST: tables of units of measurement).
  2. Pitch: a sloped roof has more area than its footprint. Multiply by the pitch factor, √(1 + (rise ÷ 12)²). For 6/12 that is 1.1180, so the roof is 1,341.641 square feet.
  3. Squares: roofers count in squares of 100 square feet: 13.42 squares, or 14.76 with 10% extra.
  4. Bundles: multiply by the bundles per square on the wrapper and round up: 45 bundles.

The same pitch factor works for a hip roof as for a gable roof, as long as every face has the same pitch: each face's area is its footprint divided by the cosine of the slope. For roofs with different pitches, work out each section separately.

Pitch factors

At a 12/12 pitch, the example roof needs 57 bundles instead of 45.

Roof area per square foot of footprint

PitchPitch factor
3/12 1.031
4/12 1.054
6/12 1.118
8/12 1.202
10/12 1.302
12/12 1.414

Bundles per square and waste

Most three-tab and architectural shingles come three bundles to a square; some heavier shingles are four, which for the example means 60 bundles. Allow about 10% extra for a simple gable roof, around 15% for hips, valleys or dormers, and more for complex roofs. The manufacturer's coverage on the wrapper takes precedence.

What this calculator does not include

  • Ridge caps, starter strip, underlayment, drip edge, flashing, ventilation and nails.
  • Tearing off the old roof, disposal and labor.
  • Roofs whose faces have different pitches. Work out each section separately and add them.

Results are estimates for planning a purchase. A roofer's measurement of your roof may differ.

Methodology and testing

Automated tests compare roof area, squares and bundles with an independent calculation, including a check that the pitch factor gives the same area as the face-by-face geometry of a hip roof. How we build and test calculators.

Sources

  • Drywall Calculator

    Wall and ceiling area less doors and windows, waste, and sheets for 4×8, 4×10 and 4×12 ft sizes, with cost.

  • Home Equity Loan Calculator

    Monthly payment, borrowing limit at common CLTV caps, cash received after closing costs, term comparison and amortization.

  • HELOC Payment Calculator

    Draw-period and repayment payments, the payment jump when repayment starts, rate what-ifs and a yearly schedule.