CalcCommons
Construction & Measurement

Roof Calculator

Estimate roof surface area, roofing squares and shingle bundles from a horizontal footprint and pitch. Add waste and an optional material price.

01 · Set it up

Your inputs

Choose a quick value or enter your own. Example inputs are filled in to get you started.

Use Roof Pitch Calculator if you measured an angle or rise and run.
Use the installed coverage on the product label; the example is one third of a roofing square.
02 · A little clarityEXAMPLE RESULT

Enter your measurements and calculate.

Calculated in your browser. Shared links include your entered values; only share information you intend to make public.

How to use

Choose a rectangular footprint or enter its known horizontal area. Include roof overhangs, select feet or meters, then enter the rise per 12. Set the waste and installed bundle coverage from your chosen product. Calculate to see surface area separately from the amount to order.

For related tasks, try the Roof Pitch Calculator.

Formula & how it works

Sloped area = horizontal projected area × √(1 + (pitch / 12)²). Roofing squares = sloped square feet / 100. Bundles = ceil(area × (1 + waste / 100) / bundle coverage).

Length40 ftWidth30 ftPitch6:12Roof surface1,341.6408 ft²
Example inputs · Horizontal projection · one uniform pitch. Schematic, not to scale.

Worked examples

Example 1

A 40 × 30 ft horizontal roof projection at 6:12 pitch has a multiplier of √1.25 ≈ 1.118. The roof surface is about 1,341.64 sq ft, or 13.42 roofing squares. With 10% waste and 33⅓ sq ft per bundle, buy 45 bundles.

Example 2

A flat 10 × 8 m projection at 0:12 pitch has 80 m² of surface. At 10% waste, allow 88 m². Bundle quantities still use the coverage entered in square feet; 1 m² is about 10.764 sq ft.

Assumptions & practical notes

Measure the entire horizontal roof projection once, including eaves. Do not double the building footprint simply because a gable roof has two slopes.

One pitch is applied to the whole projection. Split roofs with different pitches into separately measured sections; add their surface areas before deciding an order allowance.

Waste depends on cuts, valleys, hips and material layout. The example allowance is adjustable, not a manufacturer requirement. Bundles exclude ridge caps, starter strips, underlayment, flashing, fasteners and labor.

See our calculation methodology for unit definitions and testing practices.

Results are estimates for planning purposes. Verify measurements, product specifications, and applicable building codes before purchasing materials or starting work.

References & measurement guidance

Use the instructions for your selected product and the requirements that apply to your project. Example inputs are not universal specifications.

Frequently asked questions

How is this different from Roof Pitch Calculator?

Roof Pitch Calculator converts rise, run and angle. This tool uses an already-known pitch to estimate surface area and material quantities.

What is a roofing square?

One roofing square is 100 square feet of roof surface. It is an area unit, not one bundle.

Does this work for a hip roof?

It can estimate surface area when the projection and common pitch are known. Mixed slopes, dormers and nonuniform sections should be measured separately.

Can I use floor area instead?

Only when it matches the horizontal roof projection. Overhangs, porches and other roof sections can make the projection larger than floor area.

Related calculators

Roof Pitch Calculator

Convert roof rise and run, rise-in-12 pitch, or degrees into slope, angle, and slope length with a labeled diagram.

Square Footage Calculator

Add room areas and quantities, convert square units, and estimate cost per square foot.

Masonry Calculator

Estimate bricks or concrete blocks for a wall, including openings, mortar joints, multiple wythes and waste. Use preset or custom face dimensions.