How much roofing do I need?
Measure the roof footprint, multiply by the pitch factor to get the real roof surface, then add waste. Divide by 100 to get squares. Shingles are sold in bundles, and most shingles take 3 bundles per square.
Squares = footprint (sq ft) × pitch factor × (1 + waste %) ÷ 100
A 40 × 30 ft house, measured at the drip edge, with a 6/12 gable roof: 40 × 30 = 1,200 sq ft. The 6/12 pitch factor is 1.118, so the roof surface is 1,342 sq ft, or 13.4 squares. Add 10% waste for a simple gable and you need 14.8 squares, or 45 bundles of architectural shingles.
The same roof also takes 2 rolls of synthetic underlayment, 2 rolls of ice and water shield for a 3 ft course along 80 ft of eaves, 16 pieces of drip edge for 147 ft of eaves and rakes, 2 bundles of starter and 2 bundles of ridge cap for a 40 ft ridge.
Roof pitch factors
Pitch is the rise in inches for every 12 inches of run. The factor converts flat footprint area into sloped roof area.
| Pitch | Factor | 1,000 sq ft footprint becomes |
|---|---|---|
| 3/12 | 1.031 | 1,031 sq ft |
| 4/12 | 1.054 | 1,054 sq ft |
| 5/12 | 1.083 | 1,083 sq ft |
| 6/12 | 1.118 | 1,118 sq ft |
| 7/12 | 1.158 | 1,158 sq ft |
| 8/12 | 1.202 | 1,202 sq ft |
| 9/12 | 1.250 | 1,250 sq ft |
| 10/12 | 1.302 | 1,302 sq ft |
| 12/12 | 1.414 | 1,414 sq ft |
Measure the footprint including the overhangs. If parts of the roof have different pitches, add them as separate sections and enter their pitch. Don't know the pitch? Use the roof pitch calculator.
What goes on a roof besides shingles
These are the typical rules of thumb the calculator uses. Every number is editable, because coverage varies by brand.
| Material | Typical coverage |
|---|---|
| Shingles | 3 bundles per square |
| Synthetic underlayment | 10 squares per roll |
| Ice and water shield | About 200 sq ft per roll |
| Drip edge | 10 ft pieces on eaves and rakes |
| Starter strip | About 100–120 ft per bundle |
| Hip and ridge cap | About 20–33 ft per bundle |
| Nails | 4 per shingle, 6 in high-wind areas |
Ice and water shield goes along the eaves where ice dams are a risk. The IRC requires it there to reach at least 24 in inside the exterior wall, Depending on the overhang and pitch, that takes one or two 3 ft courses. Valleys get a 3 ft course too. Follow your local code and the shingle maker's instructions.
Metal roofing calculator
Metal panels are ordered by count and length, not by bundle. Divide the roof area by the panel's coverage width times its length. Exposed-fastener panels such as R-panel typically cover 36 in. Standing seam is usually 12–16 in. Panels typically run eave to ridge, so measure the slope length of each plane.
On the example roof, 36 in panels cut to 17 ft come to 29 panels, or 493 linear ft. Exposed-fastener panels take roughly 80 screws per square. Order trim, closures and flashing from your panel supplier's layout.
Free roofing calculator and app
This roofing calculator is free and works on your phone, so you can use it like an app on the roof or in the truck. Add each roof section, and your inputs are saved on your device until you change them.
Roofing estimate calculator
A roofing estimate is materials plus tear-off, disposal and labor. The calculator weighs the tear-off at roughly 250 lb per square per layer of asphalt shingles and fills dumpsters to the weight limit you enter. Labor defaults to 1.5 hours per square to install and 0.5 hours per square per layer to tear off. Steep roofs above about 8/12 go slower, so raise the hours for them.
Pricing a roofing job
Switch to contractor mode to set your labor rate and markup. The dumpster is passed through at cost. When the numbers look right, send it as a quote with the roofing estimate template.
Questions
How many bundles of shingles are in a square?
Most asphalt shingles come 3 bundles to a square, which covers 100 sq ft of roof. Some heavy architectural shingles take 4 or 5, so check the wrapper.
How do I measure a roof without climbing on it?
Measure the footprint of the house from the ground, including the overhangs, then multiply by the pitch factor. A 6/12 roof adds about 12%.
How much waste should I add for roofing?
Typically 10% for a simple gable roof and 15% or more for a hip roof or a roof with many valleys and dormers.
How many squares does a dumpster hold?
It depends on weight more than volume. One layer of asphalt shingles weighs roughly 250 lb per square, so a dumpster with a 3 ton limit holds about 24 squares of one layer.