Cedar Shake Calculator
A cedar shake calculator divides roof area by 25 sq ft per bundle (4 bundles per square). A 600 sq ft roof needs 24 bundles, or 27 with 10% waste added.
How many bundles of cedar shakes do I need?
This cedar shake calculator divides your roof’s surface area by 25 square feet, the coverage of one bundle at standard exposure. Four bundles make one roofing square of 100 sq ft. The formula is bundles = roof area ÷ 25, rounded up to a whole bundle. A 30 × 20 ft roof plane (600 sq ft) needs 24 bundles.
Enter the roof length and the slope length of the plane, not the ground footprint. Enter your price per bundle, and tick the 10% waste box to cover culls and cuts.
How the count works
Shakes overlap heavily. Only the bottom part of each piece, called the exposure, shows to the weather. The rest is covered by the courses above. Mills pack bundles so that, laid at the rated exposure, a set number of bundles covers one square. For most shake products that number is 4.
- Roof area = length × slope length of each plane, added together.
- Bundles = roof area ÷ 25.
- With waste = bundles × 1.10.
- Round up to a whole bundle, then multiply by your price.
Worked examples
- One roof plane: 30 ft × 20 ft, $60 per bundle
- Area: 30 × 20 = 600 sq ft (6 squares)
- Bundles: 600 ÷ 25 = 24 bundles, costing $1,440.00
- With 10% waste: 24 × 1.10 = 26.4, rounded up to 27 bundles, costing $1,620.00
- Whole gable roof: two planes of 40 ft × 21 ft
- Area: 2 × (40 × 21) = 1,680 sq ft (16.8 squares)
- Bundles: 1,680 ÷ 25 = 67.2, rounded up to 68 bundles, costing $4,080.00
- With 10% waste: 67.2 × 1.10 = 73.9, rounded up to 74 bundles, costing $4,440.00
Starter courses at the eaves are doubled or tripled. On long eaves, add a bundle or two on top of the waste allowance.
Bundles per square at reduced exposure
If your slope, climate, or product calls for a shorter exposure than the bundle’s rating, coverage drops in direct proportion.
| Exposure as % of rated | Coverage per bundle | Bundles per square |
|---|---|---|
| 100% | 25.0 sq ft | 4.00 |
| 90% | 22.5 sq ft | 4.44 |
| 80% | 20.0 sq ft | 5.00 |
| 75% | 18.75 sq ft | 5.33 |
To use a reduced exposure with this calculator, divide your roof area by the percentage first. At 80% exposure, a 600 sq ft roof behaves like 600 ÷ 0.80 = 750 sq ft.
How to measure a shake roof
- Measure slope length, not run. Run a tape from eave edge to ridge along the roof surface. If you can only measure from the ground, multiply the footprint by the pitch factor. That is 1.118 for a 6/12 roof, 1.202 for 8/12, and 1.414 for 12/12. The roof pitch calculator gives the factor for any slope.
- Add every plane. Hip roofs, dormers, and porches each count. The roof area calculator totals them for you.
- Measure hips and ridges separately in linear feet for cap units.
- Check the slope. Manufacturers generally set a minimum slope for shakes, often around 4 in 12, with shingles allowed somewhat lower. Below that, wood roofing is not the right product.
Common cedar shake mistakes
- Ordering by footprint. A 6/12 roof has about 12% more surface than the floor plan below it. A 12/12 roof has 41% more.
- Mixing bundle types. Shakes and sawn shingles of different lengths cover different areas. Do not use one product’s coverage for another.
- Skipping the cull pile. Expect to reject some split or tapered pieces. That is normal with natural wood and is why the waste box matters.
- Forgetting interlayment or underlayment. Budget felt or a breather mat separately. The roofing felt calculator sizes rolls.
To compare cost and coverage with other roofing, see the roofing shingle calculator for asphalt and the metal roofing calculator for panels.
Frequently asked questions
How many bundles of cedar shakes cover one roofing square?
At the manufacturer's standard exposure, most shake bundles are packed so that 4 bundles cover one square (100 sq ft). That is 25 sq ft per bundle, which is the figure this calculator uses. Always confirm the coverage on your product's label.
Does changing the exposure change how many bundles I need?
Yes, in direct proportion. Coverage scales with exposure, so a bundle laid at 80% of its rated exposure covers 80% as much roof. That raises the count from 4 to 5 bundles per square. Running past the maximum exposure saves material but can void the warranty and lead to leaks.
Are cedar shakes and cedar shingles the same product?
No. Shingles are sawn on both faces, giving a thinner, smoother, more uniform look. Shakes are split on at least one face, so they are thicker and more textured. Both are sold by the bundle, but coverage per bundle differs by product, length, and exposure, so use the figure on the label.
How much waste should I allow for cedar shakes?
Tick the 10% box for a simple gable roof. Shakes vary in width, so installers cull split or poorly shaped pieces and cut more at valleys and hips than with asphalt shingles. Cut-up roofs with several valleys and dormers often need 15% or more.
Does the bundle count include hip and ridge caps?
No. Hips and ridges use pre-assembled cap units sold by the bundle and rated in linear feet. Measure the total length of hips and ridges and order caps separately.
Do cedar shake roofs need a special underlayment?
Usually. Many shake roofs go over spaced (skip) sheathing or a ventilated mat so the wood can dry from below. Traditional shake roofs also use felt interlayment strips between courses. Requirements vary by product and local code, so check the manufacturer's instructions.
Estimates only. Verify quantities with your supplier before purchasing.