Understanding your result
The headline is the bundles to order. The stats show the bundles per square at your exposure, the area one bundle covers and the hip and ridge bundles. The breakdown scales the coverage from the product’s reference exposure, counts the field bundles with waste, adds the doubled course at the eaves and the hip and ridge units, and estimates the nails.
The number to remember is the bundles per square at your exposure. It is the figure a supplier quotes and the one that changes if the exposure changes; at the product’s maximum exposure it is 4 or 5, and it rises as the exposure shortens. If the calculator flags the exposure as too long for the product, fix that before ordering.
The same roof in asphalt is the shingle calculator, and the cost of cedar over its life against the alternatives is in the lifespan and cost per year calculator.
How we calculate this
The scaling rule is the one in the Bureau’s coverage tables: at a given exposure, a bundle of a given product covers a fixed number of square feet, and the coverage is proportional to the exposure. Twenty-four-inch shakes at the 10-inch reference exposure cover 20 square feet per bundle (five per square); at 7½ inches they cover 15 square feet, and the same roof needs a third more bundles. The guide on cedar exposure and bundles reproduces the table.
The first course at the eave is doubled (tripled for some shake installations), so the calculator adds one extra course along the eave length.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Reference coverage | 4 bundles per square for shingles, 5 for shakes, at the maximum exposure | Cedar Shake and Shingle Bureau coverage tables |
| Maximum exposures at 4/12 and steeper | 5, 5½, 7½ in (16, 18, 24 in shingles); 7½, 10 in (18, 24 in shakes) | Cedar Shake and Shingle Bureau installation manual |
| Hip and ridge | 16.7 linear ft per bundle | Typical factory hip and ridge bundle at standard exposure |
| Eave course | one extra course | CSSB installation (doubled starter course) |
| Nails | 2 per piece; average widths 8 in (shakes), 6 in (shingles) | CSSB installation manual; an estimate only |
| Waste | 10% | Estimating practice |
Assumptions last reviewed October 7, 2026.
The calculator does not count the felt interlayment for shakes, the spaced sheathing or ventilation mat, or the flashings, and it does not apply the shorter exposures needed on 3/12 to 4/12 roofs automatically: enter the shorter exposure. The guide to how long roofs last puts cedar in context with other materials.
Two worked examples
A shake roof at the standard exposure
2,000 square feet, 24-inch handsplit shakes at a 10-inch exposure, 80 feet of eaves, 40 feet of ridge, 10% waste.
- Coverage per bundle: 20 sq ft (5 bundles per square)
- Field bundles: 2,000 × 1.10 ÷ 20 = 110
- Eave course: 80 × 10 ÷ 12 ÷ 20 = 3.33 bundles
- Bundles: 114; hip and ridge: 40 ÷ 16.7 = 3 bundles
The eave course is three bundles on this roof, small but easy to forget.
A shingle roof in 18-inch Perfections
1,600 square feet, 18-inch shingles at a 5½-inch exposure, 60 feet of eaves, 30 feet of ridge, 10% waste.
- Coverage per bundle: 25 sq ft (4 bundles per square)
- Field bundles: 1,600 × 1.10 ÷ 25 = 70.4
- Eave course: 60 × 5.5 ÷ 12 ÷ 25 = 1.1 bundles
- Bundles: 72; hip and ridge: 2 bundles
Four bundles a square, against five for shakes: shingles are thinner and more pieces, but each bundle covers more.
Where to find your inputs
Product. Shingles (sawn) or shakes (split), and the length: on the bundle label, with the grade (No. 1 Blue Label for shingles, Premium for shakes).
Exposure. The product’s maximum on 4/12 and steeper; shorter on shallower roofs. Check the label and the Bureau’s table.
Roof area. The sloped area from the roof area calculator.
Eave and ridge lengths. From the plan.
Common mistakes
- One coverage for every exposure. Coverage scales with exposure. Shorter exposure, more bundles.
- Exceeding the maximum exposure. Too few layers, and the roof leaks. The calculator warns.
- No interlayment between shake courses. Shakes need it; shingles do not.
- Solid sheathing with no air. Cedar needs to dry. Spaced boards or a ventilation mat.
- Galvanized or plain steel nails. They stain and fail. Stainless steel.
- Forgetting the eave course. The first course is doubled. Add it.
Questions people ask
- How many bundles of cedar shakes per square?
- At their standard exposures, five bundles cover a square of 24-inch shakes at 10 inches or 18-inch shakes at 7½ inches, and four bundles cover a square of 16-inch shingles at 5 inches, 18-inch at 5½ or 24-inch at 7½ (Cedar Shake and Shingle Bureau). At a shorter exposure, coverage drops in proportion, so 24-inch shakes at 7½ inches need 6.7 bundles per square.
- What is the maximum exposure for cedar shingles?
- On roofs of 4/12 and steeper, the Bureau gives 5 inches for 16-inch shingles, 5½ for 18-inch and 7½ for 24-inch; for shakes, 7½ inches for 18-inch and 10 for 24-inch. On pitches from 3/12 to 4/12, shingle exposures drop (3¾, 4¼ and 5¾ inches). Longer exposures than these leave too few layers over each point of the roof.
- What is the difference between cedar shakes and shingles?
- Shingles are sawn on both faces to a smooth, tapered piece; shakes are split on at least one face, thicker and rougher. Shakes are longer-lived and rustic-looking, laid with a felt interlayment between courses; shingles are thinner, smoother and laid without interlayment. Both come in 16, 18 and 24-inch lengths and are counted by the bundle.
- How many nails for a cedar roof?
- Two per piece, stainless steel (type 316 within about 15 miles of salt water), long enough to go ¾ inch into the sheathing. Pieces per square depend on the exposure and the random widths: roughly 300 to 400 shakes or 450 to 550 shingles per square, so 600 to 1,100 nails. The calculator gives an estimate; buy by the box with a margin.
- How long does a cedar shake roof last?
- Industry surveys put cedar shakes at about 25 to 30 years and shingles a little less, longer with good ventilation and maintenance (cleaning, treatment) and shorter in damp, shaded or hot humid climates. Treated, certified products last longer; the lifespan calculator shows the cost per year against other materials.
- Does a cedar roof need special underlayment?
- Shakes are laid with an 18-inch strip of felt interlayment between each course, over the top of each shake, to shed wind-driven rain. Both shakes and shingles need air underneath: spaced sheathing (1×4 or 1×6 boards with gaps) or a ventilated mat over solid sheathing, so the wood can dry.