How it works
The calculator adds the ridge and hip lengths, adds your extra allowance and divides by the linear coverage of one bundle.
Length to cap = Ridges + Hips
Length incl. extra = Length to cap × (1 + Extra ÷ 100)
Bundles = ⌈ Length incl. extra ÷ Linear coverage per bundle ⌉
⌈ ⌉ means rounding up to the next whole bundle. Linear coverage is the length of ridge one bundle covers at the maker’s exposure: number of pieces × exposure per piece.
Where cap shingles go
Field shingles cover the roof planes. Where two planes meet at an outside edge – the ridge at the top and the hips on a hip roof – the joint is covered with cap shingles bent over the edge. Valleys, where two planes meet at an inside corner, are finished with field shingles or metal flashing and don’t take cap shingles.
A gable roof has one ridge and no hips. A hip roof on a rectangular house has one ridge and four hips; a pyramid roof has four hips and no ridge. Add every ridge and hip on the roof, including those on dormers and additions.
Measuring hips and ridges
The ridge is horizontal, so you can measure it from the ground or from the plans: on a simple gable it runs the building length plus the overhang at both rakes. Hips slope down to the eaves, so a hip is always longer than the horizontal distance it covers. Measure hips along the roof, take them from a roofing report, or work them out from the plans.
Linear coverage per bundle
Cap shingles are sold by the bundle, and each bundle states how many linear feet it covers. IKO’s data sheet for Hip & Ridge 12 and Hip & Ridge Class 4 gives 21 shingles per bundle, each split into 3 pieces, laid at 5 5/8 in exposure: 63 × 5 5/8 in = 354 in, or 29.53 linear ft (9 linear m). That is the figure in the product option. Other products have more or fewer pieces and different exposures, so their coverage differs – read the wrapper and enter your own figure.
Extra allowance
Cap shingles are laid starting at the bottom of each hip and at the end of each ridge, usually with a starter piece. Owens Corning’s ProEdge instructions, for example, start each hip and ridge with a starter shingle made from a cap shingle. Where hips meet the ridge, pieces are cut to fit. Add an allowance for these pieces, and for pieces that break when bent in cold weather.
Worked example in words
A gable roof with a 40 ft ridge and no hips needs 40 ÷ 29.53 = 1.35, so 2 bundles of IKO Hip & Ridge 12. A hip roof with a 24 ft ridge and four 18 ft hips has 96 ft to cap; with 10 % extra that is 105.6 ft ÷ 29.53 = 3.58, so 4 bundles.
Worked example
Inputs
- Ridge length
- 40 ft
- Hip length
- 0 ft
- Cap shingle
- IKO Hip & Ridge 12 / Class 4 – 29.53 lin ft (9 m) per bundle
- Extra allowance
- 0 %
Result
- Ridges and hips
- 40 ft
- Length incl. extra
- 40 ft
- Coverage per bundle used
- 29.53 ft
- Bundles
- 2
Common mistakes
- Measuring the ridge on the plan only. Hips slope down to the eaves, so a hip is longer than its horizontal length – measure along the hip or use the roof plans.
- Forgetting the hips. On a hip roof, the hips often add more length than the ridge.
- Using field shingles’ coverage. Bundles of field shingles are rated in squares of area; cap shingles are rated in linear feet.
- Assuming every bundle covers the same length. Coverage depends on the number of pieces and the exposure, which differ between products.
- Counting valleys. Valleys are covered with field shingles or metal flashing, not cap shingles.
Assumptions and limits
- Ridge and hip lengths are measured along the roof surface.
- Every foot of ridge and hip gets one layer of cap shingles at the maker’s exposure, as the bundle coverage assumes.
- Bundles are rounded up to whole bundles after the extra allowance is added.
- Starter pieces, ridge vents and hip-to-ridge junctions are not modelled separately – use the extra allowance.
Frequently asked questions
How many linear feet does a bundle of ridge cap cover?
It depends on the product. IKO’s data sheet for Hip & Ridge 12 and Hip & Ridge Class 4 gives 29.53 linear ft (9 linear m) per bundle – 21 shingles, each split into 3 pieces, laid at a 5 5/8 in exposure. Read the wrapper or data sheet of the cap shingle you buy.
How do I measure the ridge and hips?
From the roof plans, a roofing report or by measuring on the roof. A gable roof’s ridge is about as long as the building plus the rake overhangs. A hip runs from the ridge end down to the eave corner along the slope, so it is longer than its horizontal distance – measure it along the roof surface.
Do I need a starter piece on each ridge?
Many products start each hip and ridge with one. Owens Corning’s ProEdge instructions, for example, make a starter shingle from a cap shingle at the bottom of each hip and the end of each ridge. Add an extra allowance for them.
Can I cut ridge caps from 3-tab shingles instead?
Check your shingle maker’s instructions – they say which cap shingles may be used with their field shingles. If you do cut them, the coverage depends on how many pieces you get from each shingle and the exposure you use; enter that figure as your own coverage.
Sources
- Hip & Ridge Class 4 / Hip & Ridge 12 – Technical Data Sheet (04/2026) — IKO. "Shingles/Bundle 21, yielding 63 pieces"; "Coverage/Bundle 29.53 linear ft. (9 linear m)"; exposure 5 5/8 in. (63 × 5 5/8 in = 29.53 ft).
- ProEdge Hip & Ridge Shingles – installation instructions — Owens Corning. A starter shingle at the bottom of each hip and the end of each ridge ("Create a starter shingle by removing the 6 inch exposure portion of the shingle"), then shingles "with a 6 inch exposure".
Method reviewed November 4, 2026