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Ridge Cap Calculator

Bundles of cap for the ridge and the hips.

A ridge vent is not counted.

40' · 480 in · 40 ft · 12.192 m

30' · 360 in · 30 ft · 9.144 m

6/12 · 26.6° · 50%

0" · 0 in · 0 ft · 0 m

0" · 0 in · 0 ft · 0 m

1,341.64 ft²

Cutting waste on the covering — the shingles, or the metal panels. The makers allow 10% on a gable roof and 15% on a hip, where every course runs into a hip at an angle; CertainTeed's own manual says 10% is generous on a large simple roof. It moves the covering only — the starter, the cap, the drip edge and the underlayment are cut to length, not off a square.

This page recalculates as you type. There is no Calculate button.

Answer

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Bundles of ridge cap

2 bundles

1,341.64 ft² of roof, 13.42 squares, 45 bundles

Bundles of shingles 45 bundles
Roofing squares 13.42 squares
Roof area, up the slope 1,341.64 ft²
What the list comes to $2,559.50
More numbers
Footprint, on the ground 1,200 ft²
Slope factor 1.118
Bundles of starter 1 bundles
Sticks of drip edge 15 sticks
Rolls of underlayment 2 rolls
Nails 3,435 nails
DrawingThe project drawn to scale. Roof 1: 40' × 30'.40'30'Roof 1

Buying noteNo ice barrier is on this list. The code requires one where your town's table says so — look up Table R301.2 for where you are, and switch it on if it says yes.

Breakdown

Plane Measurements Qty Area on the slope Share
Roof 1 40' × 30' × 6/12 × 0" × 0" Add ×1 1,341.64 ft²

What to buy

Buying noteNo ice barrier is on this list. The code requires one where your town's table says so — look up Table R301.2 for where you are, and switch it on if it says yes.

Ways to buy the shingles

Every bundle is worked out, each rounded up to whole bundles; pick the one you will buy. The three are different shingles, not three sizes of one, so a mix means two products on one roof — buy a mix only if you meant to.

45 × bundles of HDZ Bundles 45 Left over 24.05 ft² Weight 3,501 lb Cost $1,890.00 Reference price $42.00. Type your store's.
45 × bundles of Oakridge Bundles 45 Left over 0.2 ft² Weight 3,240 lb Cost $1,710.00 Reference price $38.00. Type your store's.
45 × bundles of Landmark Bundles 45 Left over 24.05 ft² Weight 3,375 lb Cost $1,980.00 Reference price $44.00. Type your store's.

Shopping list

45 45 × bundles of HDZ $1,890.00
1 1 × bundles of OC starter $54.00 Reference price $62.00. Type your store's. Reference price $54.00. Type your store's.
2 2 × bundles of Seal-A-Ridge $96.00 Reference price $48.00. Type your store's. Reference price $56.00. Type your store's.
15 15 × sticks of drip edge $202.50 Reference price $13.50. Type your store's.
2 2 × rolls of synthetic $256.00 Reference price $128.00. Type your store's.
5 4 × 5 lb boxes of nails + 1 × 1 lb boxes of nails $61.00 Reference price $78.00. Type your store's. Reference price $14.00. Type your store's. Reference price $5.00. Type your store's.
Ticked items $2,559.50

Untick what you already have. Each row has its price beside it — type what your store charges.

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Standards

We hold the criteria and the clause, not the wording of the standard.

Meets IRC 2021 · R905.2.2

At 6/12 this roof is steep enough for asphalt shingles.

Meets IRC 2021 · R905.2.2

At 6/12 a single layer of underlayment is enough.

Meets IRC 2021 · R905.2.8.5

150' of drip edge covers the eaves and the rakes.

Not checked IRC 2021 · R905.1.2

The code requires an ice barrier only where your local Table R301.2 says so, and we hold no table by town. Look yours up and switch it on.

How this was worked out

Every number below is yours. Each constant links to the row where you can change it.

Roof 1 40' × 30' × 1.118 (6/12) 1,341.64 ft²
Squares of roof 1,341.64 ft² ÷ 100 ft² 13.42 squares

Change:A roofing square

With cutting waste 1,341.64 ft² × (1 + 10%) 1,475.8 ft²
Bundles to buy 1,475.8 ft² ÷ 33.33 ft² 45 × bundles of HDZ · 24.05 ft² over

Change:GAF HDZ bundle coversOC Oakridge bundle coversCT Landmark bundle covers

Starter course 80' ÷ 105 lf 1 × bundles of OC starter

Change:GAF Pro-Start bundle runsOC starter bundle runs

Ridge cap 40' ÷ 25 lf 2 × bundles of Seal-A-Ridge

Change:Seal-A-Ridge bundle runsOC ProEdge bundle runs

Drip edge 147' 1" ÷ (10' − 2") 15 sticks

Change:A stick of drip edgeDrip edge lap

Underlayment 1,341.64 ft² ÷ (1,001 ft² × (1 − 10%)) 2 rolls

Change:Synthetic roll coversLaps take off a roll

Nails 13.42 squares × 256 3,435 nails → 4 × 5 lb boxes of nails + 1 × 1 lb boxes of nails

Change:Nails a square

What it comes to 45 × $42.00 + 1 × $54.00 + 2 × $48.00 + 15 × $13.50 + 2 × $128.00 + 4 × $14.00 + 1 × $5.00 $2,559.50

Assumptions

Every one of these is editable. Change one and the answer changes with it.

Assumption Value Confidence
A roofing squareA roofing square is 100 ft² by the trade's definition; every shingle wrapper and every estimate is quoted in them. ≈ ft²/square Trade convention
GAF HDZ bundle coversGAF Timberline HDZ: 33.33 ft² a bundle, three bundles to the square, from the Home Depot listing. ft²/bundle From a data sheet or an agency document
OC Oakridge bundle coversOwens Corning Oakridge and Duration: 32.8 ft² a bundle. Three of them cover 98.4 ft², not 100, which is why this page never counts three bundles to the square. ft²/bundle From a data sheet or an agency document
CT Landmark bundle coversInferred, not printed: the CertainTeed Landmark data sheet gives 66 shingles to the square, and three bundles to the square is the trade's convention, so a bundle covers 100/3 ft². The sheet does not state a coverage per bundle. ~ ft²/bundle Derived or single-supplier
GAF Pro-Start bundle runsGAF Pro-Start starter strip: 120.33 linear feet a bundle, from GAF's own product page. lf/bundle From a data sheet or an agency document
OC starter bundle runsOwens Corning Starter Strip Plus: 105 linear feet a bundle, data sheet dms/10011118. lf/bundle From a data sheet or an agency document
Seal-A-Ridge bundle runsGAF Seal-A-Ridge ridge cap: 25 linear feet a bundle, from the Home Depot listing. lf/bundle From a data sheet or an agency document
OC ProEdge bundle runsOwens Corning ProEdge ridge cap: 33 linear feet a bundle, from the Home Depot combination listing. lf/bundle From a data sheet or an agency document
A stick of drip edgeDrip edge is sold in 10 ft sticks in every profile. Gibraltar Building Products catalog 2026 (AWC020926B) page 5. ft From a data sheet or an agency document
Drip edge lapDrip edge sticks lap at least 2 in, so a 10 ft stick covers 9 ft 10 in. JLC on IRC R905.2.8.5, which requires drip edge at eaves and rakes but gives the lap as a minimum rather than a number. ≈ in Trade convention
Synthetic roll coversOwens Corning ProArmor synthetic underlayment: 1,001 ft² a roll, from the Home Depot combination listing, read 14/10/2026. ft²/roll From a data sheet or an agency document
Laps take off a rollWhat the head and side laps take off a roll's printed area. A 36 in felt lapped 2 in at the head over a 36 in exposure loses about a tenth; synthetic sheets print a lap line at much the same place. An editable single number because the exact loss depends on the exposure the installer works to. ~ ratio Derived or single-supplier
Nails a squareGAF: 256 nails a square. The figure is theirs; how it divides over shingles and courses is not stated and is not inferred here. nails/square From a data sheet or an agency document
Shallowest pitch for shinglesThe floor for asphalt shingles: at this pitch and above they may be used, and from here up to the next limit the underlayment doubles. IRC R905.2.2 states both. CertainTeed's Landmark data sheet is one step stricter - "greater than 2:12" - so a roof at exactly 2:12 passes here and not on their sheet; this box is where you put their figure. rise per 12 From a data sheet or an agency document
Double underlayment belowBelow this pitch, and at or above the shallowest pitch for shingles, the underlayment has to be doubled. IRC R905.2.2; CertainTeed's Landmark data sheet states the same range. rise per 12 From a data sheet or an agency document
Hire a roofer aboveWhere a roof stops being walkable without staging. Not a code limit: it is the slope at which this page says to get a quote rather than climb up. 6:12 itself is walkable, so the warning starts above it. ≈ rise per 12 Trade convention
Cutting waste, hip15% on a hip roof: four planes means a cut at every hip. Same sources as the gable figure. A hip roof needs no second 'hip factor' on its area - the slope factor already covers the whole surface - only more cutting. ≈ ratio Trade convention

Ridge cap goes by the foot, not by the square

Ridge cap shingles are sold by the linear foot a bundle runs, and the bundles differ: GAF Seal-A-Ridge runs 25 feet, Owens Corning ProEdge runs 33. So the count is the ridge and hip length divided by whichever you are buying, rounded up.

That is why a roofing calculator has to know the roof's shape and not just its area. A 40 by 30 foot gable roof has 40 feet of ridge — two bundles of Seal-A-Ridge. The same footprint as a hip roof has 10 feet of ridge and 90 feet of hip, 100 feet in all, which is four.

Ridge and hips Seal-A-Ridge (25 lf) ProEdge (33 lf)
20 ft11
40 ft22
60 ft32
100 ft44
140 ft65

Hips take cap too

A hip is capped exactly as a ridge is, and on a hip roof the hips are much the longer run of the two. Forgetting them is the commonest way to come up short: the ridge of a hip roof looks small, so it is easy to buy for the ridge and find four corners uncovered.

A valley is the opposite case — two planes meeting the other way — and is not capped at all. It is lined, under the shingles, and these pages do not count the lining: the valley box, where a roof has two planes, runs ice barrier membrane up the valley and nothing else.

Cut cap and a ridge vent

Cutting your own cap from three-tab shingles is possible, and a bundle of three-tab yields roughly 35 linear feet that way. The manufacturers' wind warranties generally require their own cap with their own shingles, so it is worth checking before you save the bundles.

If you are fitting a ridge vent, it takes the place of cap along its own length — most vents are capped with shingle over the top, so you need cap for the vent run as well as for the bare ridge, but the vent length comes out of the plain ridge. Measure the vent, subtract it from the ridge, then add it back as capped vent: the arithmetic is the same length either way, which is why this page does not ask.