Roofing Shingle Calculator
Work out the roof area and how many bundles of shingles it takes to cover it.
Last reviewed September 19, 2026
Result
Enter footprint length and footprint width to see the result.
https://calcgallery.com/roofing/roofing-shingle-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use it
- Enter the building footprint and the roof pitch, or the sloped roof area if you already know it.
- Choose the roof shape: a hip roof wastes more than a gable.
- Check the bundles per square against what you are actually buying.
- Read the bundle count.
How it is calculated
Shingles are counted in squares of sloped roof surface:
roof area = footprint × slope factor
squares = roof area ÷ 100 ft²
bundles = ceil(squares × (1 + waste) × bundles per square)The slope factor is what turns a flat plan measurement into real roof surface. A 30 by 40 ft footprint is 1200 ft² on the ground, but at a 6 in 12 pitch the roof over it is 1342 ft², which is 13.4 squares rather than 12.
Everything then rounds up to whole bundles, because that is how they are sold, and the waste allowance is applied before the rounding rather than after.
Practical tips
Measure the footprint, including the overhangs. The eaves and rakes are roof too. Measuring to the wall rather than to the edge of the overhang typically loses a foot on every side, which on an average house is most of a square.
Order the caps separately and count the ridge. Ridge and hip caps are a different product, and on a hip roof there can be a surprising length of them. Measure every ridge and hip line in linear feet.
Buy from one production run. Shingles vary in colour between batches, and a roof patched from two lots can be visibly striped in certain light. Order the whole job at once and check the lot numbers on delivery.
Keep a bundle back. Storm damage, a cracked shingle during installation, a repair in five years. A spare bundle in the garage is worth far more than the twenty dollars it costs, because matching the colour later is often impossible.
Check the pitch against the product. Below about 4 in 12 most manufacturers require a double underlayment, and below 2 in 12 asphalt shingles should not be used at all.
This is the covering only. Sheathing, underlayment, drip edge, flashing, vents and nails are all separate, and the flashing details around chimneys and valleys are where roofs actually leak.
With your numbers
- Roof area = footprint × the slope factor = 1,341.64 ft²
- That is 13.416 squares of 100 ft²
- × 3 bundles per square, plus 10% waste, rounded up to 45
Quick reference
Shingles are cut at the rakes and the ridge, and a hip roof cuts every course, so the allowance follows the roof shape you pick.
| Job | Bundles to buy |
|---|---|
| 30 × 20 ft gable, 4 in 12 | 21 |
| 40 × 30 ft gable, 6 in 12 | 45 |
| 50 × 30 ft gable, 6 in 12 | 56 |
| 24 × 24 ft garage, 8 in 12 | 23 |
| 1500 ft² of roof, measured directly | 50 |
| 12 × 9 m gable, 6 in 12 | 43 |
| 15 × 9 m gable, 8 in 12 | 58 |
Common questions
- How many bundles of shingles do I need for a 1200 square foot roof?
- Thirty-nine bundles of three-tab at three per square, once a 10 per cent gable allowance is included. That assumes 1200 ft² of sloped roof, not of footprint. If 1200 ft² is the building footprint, a 6 in 12 pitch makes the roof 1342 ft² and you need 45.
- What is a roofing square?
- One hundred square feet of roof surface. It is the unit the whole trade quotes in, and it exists because 100 ft² is roughly what one person covers in a stretch. Three bundles of standard three-tab shingles make a square.
- Why is the roof bigger than the building?
- Because the roof is sloped and the footprint is flat. The slope factor converts one to the other. At 6 in 12 the roof is about 12 per cent larger than the footprint; at 12 in 12 it is 41 per cent larger. Ordering off the footprint is the classic way to end up three bundles short.
- How much waste should I allow?
- Ten per cent for a simple gable, fifteen for a hip. Hips waste more because every shingle meeting a hip or valley has to be cut at an angle, and the offcut is rarely usable. Complex roofs with dormers and multiple valleys can go higher again.
- Are all shingles three bundles to a square?
- No. Standard three-tab is three. Heavier architectural and designer shingles are often four or five, because a bundle is limited by what one person can carry rather than by area. Check the wrapper and change the figure if it differs.
- Does this include ridge caps, starter strip and underlayment?
- No. Ridge and hip caps are sold separately and are counted by linear feet of ridge. Starter strip runs the eaves. Underlayment, drip edge, valley flashing and nails all need working out on their own.