How many bundles of shingles do I need per square?

Most 3-tab and architectural asphalt shingles cover about 33.3 ft² per bundle, so you need 3 bundles per roofing square (100 ft²). Some heavy or designer shingles may require 4 or more bundles per square. Always check the coverage printed on the shingle wrapper and adjust the bundles-per-square field in the calculator.

How much waste should I add for a roofing project?

Waste depends on roof complexity. Simple gable roofs often use 5–7% waste, hip roofs 10–12%, and very cut-up roofs with many valleys and dormers may need 15–20%. Our roofing calculator lets you set a custom waste percentage and shows both net and adjusted areas.

What is a roofing square?

A roofing square is a unit of roof area equal to 100 square feet (about 9.29 m²). Contractors often quote roof size and price in squares. For example, a 20-square roof is 2,000 ft² of roof surface. The calculator reports both total area and squares.

Can this roofing calculator estimate material cost?

Yes. Enter your price per bundle of shingles, per roll of underlayment, and per linear foot of ridge cap. The calculator will estimate total material cost based on the roof area, waste, and your pricing. It does not include labor, tear-off, or accessories like flashing and vents.

Roofing Calculator

Q: How do I calculate roof area from house dimensions?

Measure the building length and width, multiply to get the footprint area, then multiply by the roof pitch factor. For example, a 40 ft × 30 ft house has a 1,200 ft² footprint. With a 6/12 pitch (factor ≈ 1.118), roof area ≈ 1,200 × 1.118 = 1,342 ft². Our roofing calculator does this automatically for gable, hip, and shed roofs.

Estimate roof area, roofing squares, shingle bundles, underlayment, ridge caps, and material cost for gable, hip, shed, and flat roofs.

Units

Roof type

Building length

Building width

Eave overhang (each side)

Horizontal overhang beyond wall.

Roof pitch

Rise over run (e.g., 6/12). Flat roofs use factor ≈ 1.

Waste allowance

Extra for cuts, starter, and scrap.

Shingle coverage per bundle

ft²

Typical 3-tab/architectural: ~33.3 ft² per bundle.

Ridge length (optional)

Leave blank to auto-calc for simple gable/hip.

Underlayment coverage per roll

ft²

Common 15# felt: ~200 ft² per roll.

Optional: Add material pricing

Price per shingle bundle

Price per underlayment roll

Price per ft of ridge cap

Roofing estimate

Roof area

Footprint area: –

Pitch factor: –

Net roof area: –

With waste: –

Also: –

Shingles & underlayment

Roofing squares: –

Shingle bundles: –

Underlayment rolls: –

Ridge length: –

Material cost (optional)

Shingles cost: –

Underlayment cost: –

Ridge cap cost: –

Estimated total material cost: –

Does not include labor, tear-off, flashing, vents, or permits.

Quick summary

– roof, pitch –
Approx. – squares
– bundles of shingles
– rolls of underlayment

How this roofing calculator works

This roofing calculator is designed for homeowners, contractors, and estimators who need a fast but transparent way to size a roof and estimate materials. It supports gable, hip, shed, and flat/low-slope roofs and works in both imperial (feet/inches) and metric units.

1. Roof footprint area

First we compute the horizontal footprint of the roof, including overhangs:

Footprint length = building length + 2 × overhang

Footprint width = building width + 2 × overhang

Footprint area = footprint length × footprint width

For a hip roof, this footprint is still correct; the extra area from the hips is captured by the pitch factor.

2. Pitch factor and roof surface area

Roof pitch is given as rise over run (e.g., 6/12). The pitch factor converts horizontal area to sloped surface area:

Pitch factor = \( \sqrt{1 + ( \text{rise} / \text{run} )^2 } \)

Net roof area = footprint area × pitch factor

For flat or very low-slope roofs (≤ 2/12), the factor is close to 1, so the sloped area ≈ footprint area.

3. Waste allowance

Waste accounts for starter courses, ridge caps, valleys, and off-cuts. We apply it as:

Adjusted roof area = net roof area × (1 + waste% / 100)

Typical waste allowances:

Simple gable roof: 5–7%
Hip roof: 10–12%
Complex roofs with many valleys/dormers: 15–20%

4. Roofing squares and shingle bundles

Roofers often talk in squares, where 1 square = 100 ft² ≈ 9.29 m².

Squares = adjusted roof area (ft²) ÷ 100

Bundles = adjusted roof area ÷ coverage per bundle

Most asphalt shingles cover about 33.3 ft² per bundle (3 bundles per square), but heavy or designer shingles may differ. You can override the coverage value.

5. Underlayment rolls

Underlayment (felt or synthetic) is estimated from the same adjusted roof area:

Underlayment rolls = adjusted roof area ÷ coverage per roll

Common values:

15# felt: ~200 ft² per roll
30# felt: ~100 ft² per roll
Synthetic underlayment: 400–1,000 ft² per roll

6. Ridge length and ridge caps

For simple roofs, ridge length is approximated as:

Gable roof: ridge ≈ building length
Hip roof: ridge ≈ building length − 2 × width (capped at zero)

You can override this by entering your own ridge length. Ridge cap shingles are often sold by linear foot; the calculator multiplies ridge length by your price per foot to estimate cost.

7. Material cost estimation

If you enter prices, the calculator estimates material cost:

Shingles cost = bundles × price per bundle

Underlayment cost = rolls × price per roll

Ridge cap cost = ridge length × price per linear foot

Total material cost = shingles + underlayment + ridge cap

This does not include labor, tear-off, disposal, flashing, vents, or local permit fees.

Practical tips for using the roofing calculator

Choosing the right roof type

Gable: two main slopes with a straight ridge and vertical gable walls.
Hip: all sides slope down to the walls; no vertical gables.
Shed: single sloping plane, often on additions or porches.
Flat / low-slope: nearly level roofs, often using membranes (EPDM, TPO, etc.).

Imperial vs metric roofing calculations

You can work in feet or meters. Internally, the calculator converts between:

1 ft = 0.3048 m
1 ft² ≈ 0.092903 m²
1 roofing square (100 ft²) ≈ 9.29 m²

Results are shown in both systems so you can compare to local material specs.

FAQ

How do I calculate roof area from house dimensions?

Measure the outside length and width of the building, add overhangs, multiply to get footprint area, then multiply by the pitch factor. The calculator does this automatically once you enter length, width, overhang, and pitch.

How many bundles of shingles do I need?

For most asphalt shingles, 3 bundles cover 1 square (100 ft²). If your adjusted roof area is 2,000 ft², that’s 20 squares and about 60 bundles. Always round up to whole bundles and add a bit of extra for repairs.

What waste percentage should I use?

For a simple rectangular gable roof, 5–7% is usually enough. For hip roofs or roofs with many valleys, dormers, or skylights, 10–15% is safer. If you’re unsure, ask your roofer what they typically allow for waste in your region.

Can I use this for metal or tile roofs?

Yes, for area and underlayment estimates. For metal panels or tiles, coverage per piece and waste patterns differ, so you should use manufacturer coverage tables and adjust the waste percentage accordingly.

Is this calculator accurate enough for ordering materials?

For simple roofs with good measurements, this calculator is usually accurate enough to order shingles and underlayment with a small safety margin. For complex roofs or expensive specialty materials, confirm measurements with a professional roofer or detailed roof plan before placing a large order.