Understanding your result
The headline is the bundles of cap. The stats give the length to cap before waste, either the coverage per bundle or the number of cut pieces, and the nails at two per cap. The breakdown shows the ridge and hip lengths separately, so you can see what the hips add on a hip roof, where they often total more than the ridge.
The useful number to remember is the length to cap, ridge plus hips. If the roof has a ridge vent, the same ridge length goes into the ridge vent calculator, and if you are also buying the field shingles the shingle calculator accepts the ridge and hip length and adds the cap to its order so the two agree.
For cut caps the piece count matters more than the bundle count, because it is what you will be cutting on the day: 254 pieces means 85 shingles to cut into three.
How we calculate this
The step people miss is that coverage depends on exposure. A cap piece is a 12-inch-wide shingle tab laid across the ridge; only the exposed part counts toward length, and the rest is covered by the next piece. At a 5-inch exposure 78 pieces cover 32.5 feet; at 6 inches the same pieces cover 39 feet. Purpose-made cap products set their exposure in the instructions, which is why their printed coverage is the figure to use. The shingle coverage table lists exposures and coverages for the common products.
Hips are measured along the slope, not across the plan, and the hip length is the horizontal corner-to-ridge distance (half the width on a regular hip) times the hip factor, √(rise² + 12² + 12²) ÷ 12, which is 1.50 at 6/12. The hip and valley rafter calculator gives it for any pitch.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Coverage per cap bundle | 25 linear ft | Typical of purpose-made hip and ridge cap products (manufacturers state 20 to 35 ft per bundle) |
| Shingles per three-tab bundle | 26 | Manufacturers’ bundle counts (26 to 27 shingles) |
| Caps per three-tab shingle | 3 | One per tab |
| Cap exposure (cut caps) | 5 in | The standard exposure for three-tab shingles and their cut caps |
| Nails per cap | 2 | ARMA and manufacturers’ installation instructions, one each side, 5½ to 6 in from the exposed end |
| Nail length over ridge vent | 2½ in | Ridge vent manufacturers’ instructions (nail must penetrate the deck through the vent) |
| Waste | 10% | Estimating practice for cuts at hip-ridge junctions and ridge ends |
Assumptions last reviewed October 7, 2026.
The calculator does not count the starter cap at the bottom of each hip (one cut piece per hip, inside the waste allowance) or the cap on dormer ridges unless you add their lengths. It does not know whether your cap product matches your field shingle; the wrapper does. For why the exposure sets the coverage, and how waste on hips compares with waste on field shingles, see the guide on bundles per square and waste.
Two worked examples
A gable ridge with purpose-made cap
A 44-foot ridge, no hips, cap bundles covering 25 feet, 10% waste.
- Length to cap: 44 ft
- With waste: 44 × 1.10 = 48.4 ft
- Bundles: 48.4 ÷ 25 = 1.94, rounded up to 2 bundles
- Nails: about 117 caps at a 5-in exposure × 2 = 234
Two bundles with little to spare. If the product covers 20 feet per bundle, it is three; check the wrapper before ordering.
A hip roof capped with cut three-tab shingles
A 20-foot ridge with four hips of 19 feet each (76 feet of hips), three-tab shingles cut into caps at a 5-inch exposure, 26 shingles per bundle.
- Length to cap: 20 + 76 = 96 ft
- With waste: 96 × 1.10 = 105.6 ft
- Caps per bundle: 26 × 3 = 78, covering 78 × 5 ÷ 12 = 32.5 ft
- Bundles: 105.6 ÷ 32.5 = 3.25, rounded up to 4 bundles
- Pieces: 105.6 × 12 ÷ 5 = 254 caps, 508 nails
On this roof the hips are nearly four times the ridge, which is why a hip roof costs more in cap than a gable roof of the same area. Hips are capped from the eave up and the ridge last, so the ridge caps cover the tops of the hips.
Where to find your inputs
Ridge length. On a gable roof, the house length plus both rake overhangs. On a hip roof, the house length minus the house width (for a regular hip where the ridge ends at the hip peaks). Dormer ridges are extra.
Hip length. Count the hips (four on a simple hip roof) and multiply the horizontal corner-to-ridge distance, usually half the width, by the hip factor for the pitch. Or measure one from the ground with a laser measure and multiply by the count.
Exposure and coverage. On the wrapper or the installation sheet of the cap product. For cut three-tab caps, 5 inches.
Common mistakes
- Counting only the ridge on a hip roof. The hips usually add more than the ridge. Measure all of them.
- Using the field-shingle coverage for cap. Cap is counted in linear feet at the cap exposure, not in squares. A bundle of cap covers 20 to 35 feet, not 33 square feet.
- Cutting architectural shingles for cap. They are too thick to bend over the ridge without cracking and the warranty excludes it. Buy matching purpose-made cap.
- Short nails over a ridge vent. A 1¼-inch nail through cap and vent never reaches the deck. Use 2½-inch nails and the caps stay on.
- Capping the ridge first. Hips go first, from the bottom, so the ridge caps overlap the tops of the hips and shed water the right way.
- No starter cap on the hips. The first cap at the bottom of each hip is a cut piece laid with the exposed part at the eave; without it the first full cap sits over a gap.
Questions people ask
- How many feet of ridge cap are in a bundle?
- It depends on the product and its exposure. Purpose-made cap bundles cover about 20 to 35 linear feet, with the figure printed on the wrapper; the calculator's default is 25 feet. A bundle of three-tab shingles cut into caps gives 78 pieces, which at a 5-inch exposure cover 32.5 feet.
- How many ridge cap pieces do I need per foot?
- At a 5-inch exposure, 12 ÷ 5 = 2.4 pieces per foot, so a 44-foot ridge with 10% waste takes about 117 pieces. Purpose-made cap often has a longer exposure, 5⅝ to 8 inches, so fewer pieces: at 8 inches, 1.5 per foot. Each piece takes two nails.
- Can I cut three-tab shingles for ridge cap on an architectural roof?
- Manufacturers do not allow it for the warranty, and it looks wrong: flat cut caps on a thick laminated roof. Architectural roofs take purpose-made hip and ridge cap, usually sold in bundles that match the shingle colour. Cut three-tab caps are for three-tab roofs.
- How do I measure hips without going on the roof?
- A hip runs from a corner of the eave to the ridge. Its length is the horizontal distance from that corner to the point below the ridge end (usually half the house width) multiplied by the hip factor for the pitch: 1.45 at 4/12, 1.50 at 6/12, 1.56 at 8/12 and 1.73 at 12/12. The hip and valley rafter calculator does the arithmetic.
- Does a ridge vent change the amount of cap?
- No, the cap still covers the full ridge; it goes over the vent. What changes is the nail: the cap nails must pass through the cap, the vent and into the deck, so 2½-inch nails replace the usual 1¼-inch ones. The calculator's note reminds you; the ridge vent calculator counts the vent itself.
- How much waste for ridge cap?
- About 10%. Caps are cut where each hip meets the ridge, where two hips meet at a peak, and at the ends of the ridge, and every box of cap has a few pieces broken in handling. On a plain gable ridge 5% is enough; on a hip roof with four hips meeting a short ridge, 10 to 15.