Calculate how many bundles of ridge cap shingles you need from the linear feet of ridges and hips on your roof, plus caps, nails, and estimated cost.
Ridge Cap Shingle Formula
- B is the number of bundles of ridge cap shingles to buy (rounded up)
- RL is the total ridge length in feet
- HL is the total hip length in feet
- W is the waste factor as a percent
- C is the coverage of one bundle in linear feet
- P is the number of individual caps (pieces) needed (rounded up)
- E is the cap exposure in inches
- H is one hip length in feet, BL and BW are roof eave dimensions in feet including overhangs, and p is positive roof pitch as rise per 12 inches of run
The first formula drives the main mode of the calculator. It adds the ridge and hip lengths, applies a waste factor for cuts and end caps, and divides by the coverage of one bundle to return how many bundles to buy. The second formula converts the same adjusted length into individual caps using the exposure, which is the portion of each cap left visible after the next cap overlaps it. The calculator also multiplies the estimated cap count by the entered nails per cap. The default of 2 matches the named GAF examples; use the fastening schedule for your actual product, roof and location. Starter and finishing details may require extra material.
If you do not know your ridge and hip lengths, the estimate mode uses the third formula. On a rectangular hip roof with equal pitches, each of the four hips runs diagonally from a corner up to the ridge, so its length depends on half the building width and the roof pitch. The ridge on that same roof is the absolute difference between its two eave dimensions; the shorter dimension is used for the hip formula. A square plan has a zero-length ridge. The reverse mode works in the other direction and tells you how many linear feet a given number of bundles will cover.
Bundle Coverage and Hip Length Reference
Coverage per bundle depends on the cap type and its installed exposure. The named GAF products below are the calculator presets. Other products and cut 3-tab caps use custom wrapper coverage, exposure and cap count; the wrapper and current installation instructions govern.
| Cap type | Pieces per bundle | Exposure | Coverage per bundle |
|---|---|---|---|
| Cut 3-tab example, if approved by the manufacturer | 78, assuming 26 shingles x 3 usable caps | 5 in assumed | 32.5 lin ft under these assumptions |
| GAF Seal-A-Ridge | 45 | 6-2/3 in | 25 lin ft |
| GAF TimberTex Premium | 30 | 8 in | 20 lin ft |
| CertainTeed Shadow Ridge, English format | 72 | 5 in | 30 lin ft; metric format differs |
The next table solves the hip length formula for you. It shows the length of one hip in feet by building width and pitch on a rectangular, equal-pitch hip roof. Multiply the value by 4 for the total hip length, then add the ridge (the absolute difference of the two eave dimensions). The table width must be the shorter eave dimension.
| Building width | 4/12 | 6/12 | 8/12 | 10/12 | 12/12 |
|---|---|---|---|---|---|
| 24 ft | 17.4 ft | 18.0 ft | 18.8 ft | 19.7 ft | 20.8 ft |
| 28 ft | 20.3 ft | 21.0 ft | 21.9 ft | 23.0 ft | 24.2 ft |
| 30 ft | 21.8 ft | 22.5 ft | 23.5 ft | 24.6 ft | 26.0 ft |
| 32 ft | 23.2 ft | 24.0 ft | 25.0 ft | 26.3 ft | 27.7 ft |
| 36 ft | 26.2 ft | 27.0 ft | 28.1 ft | 29.5 ft | 31.2 ft |
| 40 ft | 29.1 ft | 30.0 ft | 31.3 ft | 32.8 ft | 34.6 ft |
Example Problems
Example 1: gable roof. Your roof has a single ridge measuring 42 feet and no hips. You are using GAF Seal-A-Ridge caps that cover 25 linear feet per bundle at a 6-2/3 inch exposure, with 10% waste. Adjusted length = 42 x 1.10 = 46.2 linear feet. Bundles = 46.2 / 25 = 1.85, so you buy 2 bundles. Caps = (46.2 x 12) / (20/3) = 83.16, so the estimate is 84 caps, which takes 168 nails at 2 nails per cap.
Example 2: hip roof. The roof eaves measure 40 by 30 feet with equal 6/12 pitch on all sides. For this custom 3-tab example, assume the manufacturer permits 3 usable caps per shingle, 26 shingles per bundle and 5-inch exposure. Ridge = 40 – 30 = 10 feet. Each hip = (30/2) x √(2 + 0.25) = 15 x 1.5 = 22.5 feet, and four hips total 90 feet. Total length = 100 feet, and with 10% waste you need 110 linear feet. Under those assumptions, a bundle yields 32.5 linear feet of caps, so 110 / 32.5 = 3.4, which rounds up to 4 bundles. At a 5-inch exposure that is 264 caps and 528 nails.
FAQ
How many linear feet does a bundle of ridge cap shingles cover?
GAF Seal-A-Ridge covers 25 linear feet with 45 caps at 6-2/3-inch exposure. GAF TimberTex covers 20 linear feet with 30 finished caps at 8-inch exposure. Other products vary. The 32.5-foot cut 3-tab example assumes 26 shingles, 3 usable caps each and 5-inch exposure; enter your actual approved package data instead of assuming this yield. Check the current wrapper and installation instructions before ordering.
Can you cut 3-tab shingles into ridge caps?
Yes. A 36-inch 3-tab shingle cuts into three 12 inch caps, and installers usually taper the cut slightly so the hidden portion is narrower than the exposed portion. Use cut caps only where the shingle manufacturer’s installation instructions approve them, with the required exposure and starter/finishing details. Otherwise use its specified matching hip and ridge product. Appearance, installation and warranty requirements depend on the product.
What nails should you use for ridge caps?
Use the nail type, length, penetration, placement and sealing specified for the actual cap product and any ridge vent. GAF Seal-A-Ridge and TimberTex instructions specify two nails per finished cap plus product-specific starter, final-cap and sealing details. Do not assume that a universal four-nail high-wind rule applies. Check current manufacturer instructions and local requirements.
