How many bundles of shingles are in a square?

Counting three bundles of 3-tab shingles to a square and four of architectural shingles to a square, which is where the 33.3 and 25 square feet per bundle come from. A square is 100 square feet of finished roof, so the count is packaging rather than area: the same 100 square feet takes three bundles of one profile and four of the other. Manufacturers do vary, so read the wrapper — if it says 32.3 square feet per bundle, type that into the coverage box and the count will follow.

What is a roofing square?

100 square feet of finished roof, and it is the unit roofers quote in. A 2,121 square foot roof is 21.2 squares; with the wastage allowance this page adds, the order is written as 24.4 squares. Squares are a unit of area, so they do not change when you change the shingle profile — only the bundle count does, because bundles are a unit of packaging.

How much wastage should I allow on a roof?

10% is the usual starting point on a plain gable, 15% once the roof has valleys, dormers, skylights or a lot of penetration flashing, and slightly less than 10% on a simple shed roof. The allowance covers off-cuts, ridge and hip caps, the starter course and mistakes. It does not cover valley metal, drip edge or the ice-and-water membrane at the eaves — those are separate line items, and on a real order they usually add up to more than the waste does.

Felt or synthetic underlayment — how many rolls?

Felt at four squares per roll and synthetic membrane at ten squares per roll, which is the usual packaging: a 1,181 square foot roof wants three rolls of 15 lb felt or two of synthetic, and a 696 square foot roof wants two rolls of felt but only one synthetic. Synthetic is lighter, tears less on a steep roof and is the only sensible choice below about 4:12, where felt is normally doubled or replaced by a self-adhered membrane.

Does the pitch change the number of bundles?

Yes, through the roof area. The plan is stretched by the pitch multiplier before anything is counted: 4:12 stretches it by 1.0541, 6:12 by 1.118 and 12:12 by 1.4142, so the same footprint takes 34% more material at the steep end than at the shallow end. The pitch field here is a dropdown of the eight pitches that turn up on materials lists; if the drawing calls out a fractional pitch, get the roof area from the roof pitch calculator and use it as your plan size here.

Why is the count on this page different from the supplier's?

Usually the coverage figure rather than the arithmetic. This page counts off the industry's usual coverage — three bundles of 3-tab or four of architectural to a square — while a supplier counts off the profile actually being delivered, which can differ by about a tenth either way. The wastage allowance is the other lever, and it is a field for that reason. Treat this page as the sanity check that catches an order of the wrong order of magnitude, and the supplier's take-off as the one that gets signed.

Roofing Calculator

Result

Bundles of shingles

Roofing squares (100 ft² each): 11.8
Roof area in square feet: 1,073 ft²
Roof area in square metres: 99.71 m²
Rolls of underlayment: 3

Roofing calculator: give it the pitch, the plan size and the wastage you are willing to carry, and it returns the three numbers a roofing order is actually written in — bundles of shingles, squares and rolls of underlayment. Everything on the page comes from one figure, the roof area, and the roof area is built in two steps: the plan is stretched by the pitch multiplier, then stretched again by the waste allowance that pays for the hips, the valleys and the cuts around vents and chimneys. The bundles are then counted off the coverage of the shingle you picked, three bundles of 3-tab to a square at 33.3 square feet each and four bundles of architectural shingles at 25 square feet — which is why the same roof needs 36 bundles of one and 48 of the other, and why the profile is a field on this page rather than a footnote. Underlayment is bought by the roll and the rolls are far bigger than people expect: 15 lb felt covers 4 squares and a synthetic membrane covers 10, so a house roof that wants three rolls of felt may want only one of synthetic. The pitch is a dropdown of the eight pitches that appear on materials lists, because it changes the roof area and therefore every count on the page. If the drawing calls out a fractional pitch — 6.5:12, 4.75:12 — or you want the angle, the rafter length and the roof area on their own, the roof pitch calculator in this section takes any slope as a number; this page is the one to use when you are writing the order, and it is the only one of the two that knows about shingle profiles, underlayment and waste.

What one bundle or roll covers

Material	Coverage per unit (ft²)	Units per 10 squares	Units per 100 m²
3-tab shingles	33.33	30	32.29
Architectural (laminate) shingles	25	40	43.06
15 lb felt underlayment	400	2.5	2.69
Synthetic underlayment	1000	1	1.08

A square is 100 square feet of finished roof, which is how roofers quote; the second column turns a package into area, and the third turns it into an order — the third column is the one to multiply your own square count by. The fourth column is the same figure in square metres, for a take-off written metrically: 100 m² is 1,076 square feet, so it wants about 8% more units than the same number of squares. These are the industry's usual packaging figures and the wrapper always wins: if the bundle in front of you covers a different area, use the coverage field on the page instead of this chart.

Formula

Roof area = length × width × M, then × (1 + wastage ÷ 100); bundles = roof area ÷ coverage per bundle

L: Length of the roof plan, along the ridge, in feet
W: Width of the roof plan, eave to eave, in feet
M: Pitch multiplier for the pitch selected: √(144 + p²) ÷ 12
w: Wastage allowance as a percentage of the roof area
c: Coverage of one bundle or one roll, in square feet

Use it when the roof geometry is settled and the question has become commercial: how much shingle, how much underlayment, how many squares to quote. The order of the two multiplications matters to nobody's arithmetic but matters to the answer — the wastage allowance applies to the roof area, not to the plan, so a steep roof wastes more material in absolute terms for the same percentage. A 10% allowance is the usual starting point on a plain gable; a roof with valleys, dormers, skylights or a lot of penetration flashing is usually taken at 15%, and a simple shed roof with two cuts can come in under 10%. If you do not yet know the pitch, or the roof is not a plain rectangle, start with the roof pitch calculator in this section and come back with the area — this page takes the plan size and does not care how many planes the roof actually has.

Worked examples

A 6:12 gable roof, 40 ft by 24 ft, in 3-tab shingles over felt
1. Multiplier for 6:12: √(144 + 36) ÷ 12 = 1.118
2. Roof area: 40 × 24 × 1.118 = 1,073 square feet (99.71 m²)
3. With 10% wastage: 1,073 × 1.1 = 1,181 square feet
4. Bundles: counting three bundles of 3-tab to a square, one bundle covers 33.33 ft², so 1,181 ÷ 33.33 = 35.4 → 36 bundles
5. Squares: 1,181 ÷ 100 = 11.8
6. Underlayment: 15 lb felt covers 400 ft² a roll, so 1,181 ÷ 400 = 2.95 → 3 rolls
This is the page's default setting. The two counts move independently of each other: change the shingle to architectural and the bundles jump to 48 while the squares stay at 11.8, because a square is a unit of area and a bundle is a unit of packaging.
A low 4:12 roof in architectural shingles over synthetic membrane
1. Multiplier for 4:12: √(144 + 16) ÷ 12 = 1.0541
2. Roof area: 30 × 20 × 1.0541 = 632 square feet (58.76 m²)
3. With 10% wastage: 696 square feet
4. Bundles: at 25 ft² per bundle of architectural shingles, 696 ÷ 25 = 27.8 → 28
5. Underlayment: a synthetic roll covers 1,000 ft², so 696 ÷ 1,000 = 0.7 → 1 roll
A low slope is where the underlayment choice shows up most: the same roof that wants three rolls of 15 lb felt wants a single roll of synthetic membrane. Below 4:12 most codes stop accepting felt alone and require either a double layer or a self-adhered membrane — this page counts rolls, and does not judge which system your roof needs.
A steep 12:12 roof, 50 ft by 30 ft, with a 15% allowance
1. Multiplier for 12:12: √(144 + 144) ÷ 12 = √2 = 1.4142
2. Roof area: 50 × 30 × 1.4142 = 2,121 square feet (197.08 m²)
3. With 15% wastage: 2,121 × 1.15 = 2,439 square feet
4. Bundles: 2,439 ÷ 33.33 = 73.2 → 74
5. Squares: 2,439 ÷ 100 = 24.4
6. Underlayment: 2,439 ÷ 400 = 6.1 → 7 rolls
The 45° roof is 41% bigger than its plan, and at 15% wastage the order is another 15% on top of that — 74 bundles against the 64 that the plan alone would suggest. Steep roofs also cut slower and waste more off-cuts, which is the practical reason the allowance climbs with the pitch even though the percentage is a field you set yourself.

Limitations

The counts are an estimating aid, not a materials take-off. The geometry part is exact — plan area times the pitch multiplier — but every number that follows it rests on packaging figures that are magnitudes rather than specifications. Coverage per bundle varies by about a tenth between manufacturers and by more between profiles, so 33.3 and 25 square feet are the industry's usual figures, not the ones printed on the wrapper in front of you: the wrapper always wins, and the box on this page is a field you can leave alone or overwrite with the number you actually bought. The underlayment rolls are the same story at a bigger scale — felt is sold in 4-square rolls and synthetic membrane in 10-square rolls, but both come in other sizes. The wastage allowance is a flat percentage applied to the whole roof, which is a rough way to account for hips, valleys, dormers and penetration flashing: on a complicated roof it under-counts, and on a plain rectangle it over-counts. Ridge caps, starter course, drip edge, valley metal, nails and the ice-and-water membrane at the eaves are not counted here at all, and on a real order they add up to more than the waste allowance does. Finally, the roof is treated as one rectangle. A hip roof, an L-shaped plan or a roof that steps down over a garage has to be split into rectangles and run through the page more than once — the total will be larger than a single pass through the overall footprint, and that difference is exactly the sort of thing this page cannot see.

Frequently asked questions

How many bundles of shingles are in a square?: Counting three bundles of 3-tab shingles to a square and four of architectural shingles to a square, which is where the 33.3 and 25 square feet per bundle come from. A square is 100 square feet of finished roof, so the count is packaging rather than area: the same 100 square feet takes three bundles of one profile and four of the other. Manufacturers do vary, so read the wrapper — if it says 32.3 square feet per bundle, type that into the coverage box and the count will follow.
What is a roofing square?: 100 square feet of finished roof, and it is the unit roofers quote in. A 2,121 square foot roof is 21.2 squares; with the wastage allowance this page adds, the order is written as 24.4 squares. Squares are a unit of area, so they do not change when you change the shingle profile — only the bundle count does, because bundles are a unit of packaging.
How much wastage should I allow on a roof?: 10% is the usual starting point on a plain gable, 15% once the roof has valleys, dormers, skylights or a lot of penetration flashing, and slightly less than 10% on a simple shed roof. The allowance covers off-cuts, ridge and hip caps, the starter course and mistakes. It does not cover valley metal, drip edge or the ice-and-water membrane at the eaves — those are separate line items, and on a real order they usually add up to more than the waste does.
Felt or synthetic underlayment — how many rolls?: Felt at four squares per roll and synthetic membrane at ten squares per roll, which is the usual packaging: a 1,181 square foot roof wants three rolls of 15 lb felt or two of synthetic, and a 696 square foot roof wants two rolls of felt but only one synthetic. Synthetic is lighter, tears less on a steep roof and is the only sensible choice below about 4:12, where felt is normally doubled or replaced by a self-adhered membrane.
Does the pitch change the number of bundles?: Yes, through the roof area. The plan is stretched by the pitch multiplier before anything is counted: 4:12 stretches it by 1.0541, 6:12 by 1.118 and 12:12 by 1.4142, so the same footprint takes 34% more material at the steep end than at the shallow end. The pitch field here is a dropdown of the eight pitches that turn up on materials lists; if the drawing calls out a fractional pitch, get the roof area from the roof pitch calculator and use it as your plan size here.
Why is the count on this page different from the supplier's?: Usually the coverage figure rather than the arithmetic. This page counts off the industry's usual coverage — three bundles of 3-tab or four of architectural to a square — while a supplier counts off the profile actually being delivered, which can differ by about a tenth either way. The wastage allowance is the other lever, and it is a field for that reason. Treat this page as the sanity check that catches an order of the wrong order of magnitude, and the supplier's take-off as the one that gets signed.

References

Approximate Conversions from U.S. Customary Measures to Metric — the chart behind the square feet, squares and square metres on this page — National Institute of Standards and Technology
The International System of Units (SI) brochure — the square metre the roof area and the coverage figures are converted to — Bureau International des Poids et Mesures (BIPM)

Related calculators

Roof Pitch CalculatorRoof pitch to angle, multiplier, rafter length and roof area.Elevation Grade CalculatorGrade and slope percentage from a rise over a run.Square Footage CalculatorSquare footage of a room or an irregular floor plan.Asphalt CalculatorAsphalt tonnage for a driveway from area and depth.