Roofing Calculator

By Taro Schenker | Updated February 11, 2026

Quick Answer: To calculate roofing materials, multiply (Length + 2 x Overhang) x (Width + 2 x Overhang) x Pitch Multiplier to get roof area, then divide by 100 for squares. Common pitch multipliers: 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 12/12 = 1.414. Each square needs 3 bundles of shingles. Underlayment rolls cover 400 sq ft each. Drip edge comes in 10 ft pieces. Material weights per square: asphalt 250 lbs, metal 100, clay tile 900, slate 700, TPO/EPDM 50. Add 15% waste for standard roofs. A 30 x 40 ft building with 6/12 pitch needs about 15.5 squares (47 bundles).

Calculate how much roofing material you need for your project. Enter your building dimensions, select your roof type and pitch, and get the exact number of squares, bundles, underlayment rolls, drip edge pieces, total weight, and estimated cost.

How to Calculate Roofing

The formula for calculating roofing material starts with your footprint area and adjusts for roof pitch:

Roof Area = (Length + 2 × Overhang) × (Width + 2 × Overhang) × Pitch Multiplier

The pitch multiplier accounts for the extra surface area created by the slope of the roof. A steeper pitch means more roof area to cover. For example, a 6/12 pitch adds about 11.8% more area compared to a flat roof, while a 12/12 (45-degree) pitch adds 41.4%.

Measure the building length and width (footprint dimensions).
Add the eave overhang to each side (typically 6-18 inches).
Multiply by the pitch multiplier for your roof slope.
Divide by 100 to convert square feet to roofing squares.
Add 15% for waste (more for complex roof shapes).
Multiply squares by 3 to get the number of shingle bundles.

Roof Pitch Multiplier

The pitch multiplier converts your building footprint area to actual roof surface area. Use this table to understand how slope affects material quantity:

Pitch	Multiplier	Angle
2/12	1.014	9.5°
4/12	1.054	18.4°
6/12	1.118	26.6°
8/12	1.202	33.7°
10/12	1.302	39.8°
12/12	1.414	45.0°

Roofing Material Comparison

Compare costs, weights, and lifespan for the most common roofing materials:

Material	Cost / Square	Weight / Square	Lifespan
Asphalt Shingles	$300-500	250 lbs	20-30 years
Metal Panels	$600-1,200	100 lbs	40-70 years
Clay / Concrete Tile	$800-1,800	900 lbs	50-100 years
Slate	$1,000-3,000	700 lbs	75-200 years
TPO / EPDM	$400-600	50 lbs	20-30 years

Formula Summary

Roof Area Formula: Calculate the total roof surface area by adjusting the building footprint with overhang and pitch multiplier.

$$A_{\text{roof}} = (L + 2 \times O)(W + 2 \times O) \times M_{\text{pitch}}$$

where $O$ = eave overhang (ft) and $M_{\text{pitch}} = \sqrt{1 + (\frac{\text{rise}}{12})^2}$.

Squares: $$\text{Squares} = \frac{A_{\text{roof}}}{100}$$

Bundles: $$\text{Bundles} = \lceil \text{Squares} \times (1 + W\%) \times 3 \rceil$$

Underlayment: $$\text{Rolls} = \lceil \frac{A_{\text{roof}}}{400} \rceil$$ Drip Edge: $$\text{Pieces} = \lceil \frac{2(L + W)}{10} \rceil$$

Pitch	Multiplier	Material	Weight/Square
2/12	1.014	Asphalt Shingles	250 lbs
4/12	1.054	Metal Panels	100 lbs
6/12	1.118	Clay / Concrete Tile	900 lbs
8/12	1.202	Slate	700 lbs
10/12	1.302	TPO / EPDM	50 lbs
12/12	1.414

Standard Assumptions: Waste factor of 15% for simple gable/shed roofs; 20% for hip roofs with valleys and dormers. 3 bundles per roofing square. Underlayment roll covers 400 sq ft. Drip edge pieces are 10 ft long. Flat roofs use a pitch multiplier of 1.0.

Related Calculators

Shingle Calculator — calculate shingles for your specific roof dimensions
Plywood Calculator — estimate plywood sheets for roof decking
Insulation Calculator — calculate insulation for attics and walls

Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.

Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.

Frequently Asked Questions

What is a roofing square?▾

A roofing square is a unit of measurement equal to 100 square feet of roof area. Roofing materials like shingles and underlayment are sold by the square. For example, a 2,000 square foot roof requires 20 squares of shingles before accounting for waste.

How many bundles of shingles do I need per square?▾

Standard asphalt shingles require 3 bundles per square (100 sq ft). Some heavier architectural shingles may require 4 or 5 bundles per square. Our calculator uses the standard 3-bundle-per-square ratio and adds your specified waste factor on top.

What waste factor should I use for roofing?▾

Use 10-15% waste factor for simple gable or shed roofs with few penetrations. Use 15-20% for hip roofs or roofs with multiple valleys, dormers, and skylights. Complex roof shapes with many cuts can require up to 25% waste factor.

How do I determine my roof pitch?▾

Roof pitch is expressed as rise over run — for example, a 6/12 pitch means the roof rises 6 inches for every 12 inches of horizontal run. You can measure pitch from the attic using a level and tape measure, or from outside using a pitch gauge. A 6/12 pitch is the most common residential roof slope.

How much does a new roof cost?▾

Asphalt shingle roofs typically cost $300-500 per square installed. Metal roofing runs $600-1,200 per square. Clay tile costs $800-1,800 per square, and slate ranges from $1,000-3,000 per square. Costs vary by region, roof complexity, and whether the old roof needs to be removed first.

How long do different roofing materials last?▾

Asphalt shingles last 20-30 years (architectural shingles closer to 30). Metal roofing lasts 40-70 years. Clay and concrete tile can last 50-100 years. Slate is the most durable at 75-200 years. TPO and EPDM flat roofing membranes typically last 20-30 years.