Find a tool

Roofing Calculator

Footprint and pitch in; bundles, starter, ridge, drip edge and underlayment out.

No labour, tear-off or flashing.

1,341.6 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

Save imageExcel

Bundles of shingles

45 bundles

1,341.6 ft² of roof, 13.42 squares, 45 bundles

Roofing squares 13.42 squares
Roof area, up the slope 1,341.6 ft²
What the list comes to $2,207.00
More numbers
Footprint, on the ground 1,341.6 ft²
Slope factor 1
Bundles of starter 0 bundles
Sticks of drip edge 0 sticks
Rolls of underlayment 2 rolls
Nails 3,435 nails

Buying noteAn area typed in is a roof measured up the slope, not an outline, so it has no eave, rake or ridge. The shingles, the underlayment and the nails count it; the starter, the ridge cap and the drip edge cannot. Enter the roof as a footprint and a pitch if you need those.
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
Area 1 1,341.6 Add ×1 1,341.6 ft²

What to buy

Buying noteAn area typed in is a roof measured up the slope, not an outline, so it has no eave, rake or ridge. The shingles, the underlayment and the nails count it; the starter, the ridge cap and the drip edge cannot. Enter the roof as a footprint and a pitch if you need those.
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 24.09 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 0.24 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 24.09 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
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 $2,207.00

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

Save imageExcel

Standards

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

Not checked IRC 2021 · R905.2.2

No plane here has measurements that make a roof.

Not checked IRC 2021 · R905.2.2

No plane here has measurements that make a roof.

Not checked IRC 2021 · R905.2.8.5

No plane here has measurements that make a roof.

Not checked IRC 2021 · R905.1.2

No plane here has measurements that make a roof.

How this was worked out

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

Area 1 1,341.6 1,341.6 ft²
Squares of roof 1,341.6 ft² ÷ 100 ft² 13.42 squares

Change:A roofing square

With cutting waste 1,341.6 ft² × (1 + 10%) 1,475.76 ft²
Bundles to buy 1,475.76 ft² ÷ 33.33 ft² 45 × bundles of HDZ · 24.09 ft² over

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

Starter course 0" ÷ 0 lf

Change:GAF Pro-Start bundle runsOC starter bundle runs

Drip edge 0" ÷ (10' − 2") 0 sticks

Change:A stick of drip edgeDrip edge lap

Underlayment 1,341.6 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 + 2 × $128.00 + 4 × $14.00 + 1 × $5.00 $2,207.00

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

What a roof takes, and why the edges matter

A roof is bought in two ways at once. The field — the shingles, the underlayment, the nails — goes by area. Everything else goes by edge: starter strip along the eaves, ridge cap along the ridge and the hips, drip edge along the eaves and the rakes, ice barrier up from the eaves. Get the area and you can count bundles. Get the edges and you can count the other five things, which is most of the list.

So this page asks for a footprint and a pitch, and works the edges out of them. A 40 by 30 foot gable roof at 6:12 has 80 feet of eave, 40 feet of ridge, and four rakes of 16 feet 9 inches each — 67 feet of rake altogether, because a rake runs up the slope and the slope is longer than the plan.

From footprint to roof area

Roof area is the footprint times the slope factor, which is √(rise² + 144) ÷ 12. At 6:12 that is 1.118, so 1,200 square feet of footprint is 1,341.6 square feet of roof — 13.42 squares, a square being 100 square feet.

PitchSlope factorDegrees
3:121.030814.0°
4:121.054118.4°
6:121.118026.6°
8:121.201933.7°
9:121.250036.9°
12:121.414245.0°

The footprint to use is the one measured to the drip edge, overhangs included — that is what the roof actually covers. If you measured the walls instead, put the overhang in the two boxes and the page adds it: the eave overhang widens the roof across the slope, the rake overhang lengthens it along the ridge.

Bundles, not three to the square

A bundle of shingles is roughly a third of a square, and the usual shorthand is three bundles to the square. It is wrong for some shingles: an Owens Corning Oakridge bundle covers 32.8 square feet, so three of them cover 98.4, not 100 — about two per cent short over a whole roof. This page divides by the coverage printed on the wrapper, and the table of ways to buy lets you pick the bundle you are actually buying.

Cutting waste is on top: the makers allow 10 per cent on a gable roof and 15 on a hip, where every plane meets another at an angle. That box is yours to change — on a big simple roof the manufacturers' own manuals say 10 per cent is generous.

Measuring the pitch

Hold a level against the slope, mark 12 inches along it, and measure down from that mark to the roof. That drop is the rise. A drop of 6 inches over 12 is a 6:12 roof. You can type it any way you have it — 6, 6/12, 6:12, 26.6° or 50% — and the line under the box prints all three, so you can see at once whether the slope it read is the slope you meant.

What this page does not do

It does not price labour or tearing off the old roof, and it does not count flashing around a chimney, a skylight or a wall. It also adds the edges of several planes up as if they were separate roofs: where two planes meet, the edge between them is neither eave nor rake, so a complicated roof entered as several pieces will read high on starter, cap and drip edge. For a single gable, hip or shed it counts every edge the roof has.