Roofing Calculator — Area, Squares & Materials

Material	Quantity	Coverage
Composition shingles	74	~33 ft² per bundle
Roll roofing	25	~36 in × 36 ft per roll
#15 felt	7	~36 in × 144 ft per roll
#30 felt	13	~36 in × 72 ft per roll

Material

Quantity

Coverage

Composition shingles

~33 ft² per bundle

Roll roofing

~36 in × 36 ft per roll

#15 felt

~36 in × 144 ft per roll

#30 felt

~36 in × 72 ft per roll

Estimate the sloped area of a roof from the house footprint, pitch or angle, and eave overhang, then convert that area into US shingle, roll-roofing, and felt counts. Use the materials tab when you already know the roof surface.

Formula

Lengths use the international foot (1 ft = 0.3048 m). The house footprint is treated as a rectangle whose perimeter is 10% longer than a square of the same area, then expanded by the eave overhang:

plan   = A + 4.4 × eaves × (√A + eaves)
pitch  = √(1 + (rise/12)²)
angle  = 1 / cos(θ)
roof   = plan × pitch (or angle)

A 6/12 pitch is rise 6, so √(1 + 0.5²) = 1.118. A 25° roof uses 1 / cos(25°) ≈ 1.103. Materials are counted on the sloped area in square feet:

squares (10% extra) = ceil(roof_ft² × 1.1 / 100)
shingle bundles     = ceil(roof_ft² × 3 / 100)
roll roofing        = ceil(roof_ft² / 100)
#15 felt            = ceil(roof_ft² / 400)
#30 felt            = ceil(roof_ft² / 200)

Complex roofs (hips, valleys, dormers) are more accurate when you measure each plane and add the areas — use the Area Calculator for those pieces, then paste the total into the materials tab.

Typical slope correction factors

Pitch	Angle	Multiply by	Pitch	Angle	Multiply by
1/12	4.8°	1.003	2/12	9.5°	1.014
3/12	14.0°	1.031	4/12	18.4°	1.054
5/12	22.6°	1.083	6/12	26.6°	1.118
7/12	30.3°	1.158	8/12	33.7°	1.202
9/12	36.9°	1.250	10/12	39.8°	1.302
11/12	42.5°	1.357	12/12	45.0°	1.414
13/12	47.3°	1.474	14/12	49.4°	1.537
15/12	51.3°	1.601	16/12	53.1°	1.667
17/12	54.8°	1.734	18/12	56.3°	1.803
19/12	57.7°	1.873	20/12	59.0°	1.944
21/12	60.3°	2.016	22/12	61.4°	2.088
23/12	62.4°	2.162	24/12	63.4°	2.236

Ceramic tile has no standard coverage. Ask a contractor or the tile maker for pieces per square. Shingle roofs last about 15–30 years, membrane roofs 5–15 years, and ceramic tile can last 100 years or more.

Examples

Default 2,000 sq ft house, 6/12, 1 ft eaves

House base 2,000 sq ft, pitch 6/12, eaves 1 ft. Estimated roof area is 2,461 square feet (228.6 m², 273.4 yd²). With a 10% buffer that is 28 roof squares, 74 bundles of composition shingles, 25 rolls of roll roofing, 7 rolls of #15 felt, and 13 rolls of #30 felt. At $3 per square foot the material price is $7,383.

Same house, no eaves

Pitch 6/12 and eaves 0 on 2,000 sq ft is 2,236 square feet (207.7 m²). That is 25 squares and 68 shingle bundles.

Known 2,000 sq ft roof surface

On the materials tab, 2,000 sq ft of roof (already sloped) needs 22 squares with buffer, 60 shingle bundles, 20 rolls of roll roofing, 5 rolls of #15 felt, and 10 rolls of #30 felt.

Frequently asked questions

How do I calculate roof area from the house footprint?

Start with the house base area (the land the house covers), add eaves overhang, then multiply by a slope factor. A 2,000 sq ft footprint with 1 ft eaves and a 6/12 pitch is 2,461 sq ft of roof (228.6 m²). The slope factor is √(1 + (rise/12)²), or 1 / cos(θ) when you enter an angle.

What is a roofing square?

One square is 100 square feet of roof. Contractors order by the square. This calculator adds a 10% waste buffer, so 2,461 sq ft is 28 squares (2,461 × 1.1 / 100, rounded up). The 2,000 sq ft materials example is 22 squares.

How many bundles of shingles do I need?

Three bundles cover one square (~33 ft² each). Divide roof area by 100, multiply by 3, and round up. The default 2,461 sq ft roof needs 74 bundles. A known 2,000 sq ft roof needs 60 bundles. Always confirm coverage on the wrapper — architectural shingles can differ.

How does roof pitch change the area?

Steeper roofs have more surface than the floor plan. A 6/12 pitch multiplies the plan by 1.118; 12/12 (45°) by 1.414; 24/12 by 2.236. On 2,000 sq ft with no eaves, 6/12 is 2,236 sq ft and 12/12 is 2,828 sq ft.

Does the price include labor or tear-off?

No. The optional price is materials only, using the unit you enter (per square foot, metre, yard, inch, or centimetre), rounded to the nearest dollar. Labor, tear-off, underlayment extras, and delivery are not included.

Formula

Typical slope correction factors

Examples

Frequently asked questions

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