Roofing Calculator

1. Select the roof complexity: simple for a gable or shed roof, moderate for a hip roof, or complex for a roof with valleys, dormers or multiple angles.
2. Select the shingle type: 3-tab (3 bundles per square) or architectural/dimensional (4 bundles per square).
3. Enter the footprint length and width in feet. This is the building outline, not the roof surface.
4. Select the roof pitch from the dropdown. If you do not know your pitch, measure the rise per 12 inches of horizontal run.
5. Optionally enter the price per bundle to see a cost estimate.

Here is what each result line means:

For a full framing material list including rafters and sheathing, see the framing calculator.

A roofing calculator estimates the number of shingle squares and bundles you need to cover a roof. It starts with the building footprint area, applies a pitch multiplier to account for the slope of the roof, adds a waste allowance for the roof complexity, and then converts the total area into roofing squares and bundles.

Roofing materials are sold by the square. One roofing square covers 100 square feet of roof surface. A standard 3-tab shingle package contains about 33.3 square feet (3 bundles per square), while heavier architectural shingles may require 4 bundles per square depending on the manufacturer.

The calculator converts a flat building outline into a sloped roof area in four steps.

Step 1: Pitch Multiplier

The pitch multiplier accounts for the extra surface area created by the roof slope. A flat roof (0/12) has a multiplier of 1.000, and a 12/12 (45-degree) roof has a multiplier of 1.414.

Step 2: Roof Area

Multiply the building footprint area (length times width) by the pitch multiplier. The result is the true roof surface area that needs to be covered with shingles.

Step 3: Waste Allowance

Add waste for starter strips, ridge caps, hip caps, valleys, and cutting losses. A simple gable roof wastes about 10%, a hip roof 15%, and a complex roof with dormers and valleys 20%.

Step 4: Squares and Bundles

Divide the total area by 100 to get roofing squares. Round up to the next whole square. Multiply by 3 bundles per square for 3-tab shingles or 4 bundles per square for architectural shingles.

A simple gable roof over a building that is 40 ft long and 37.5 ft wide, with a 6/12 pitch and 3-tab shingles.

Step 1. Footprint area = 40 x 37.5 = 1,500 sq ft.

Step 2. Pitch multiplier = sqrt(1 + (6/12)^2) = sqrt(1.25) = 1.118.

Step 3. Roof area = 1,500 x 1.118 = 1,677 sq ft.

Step 4. With 10% waste = 1,677 x 1.10 = 1,845 sq ft.

Step 5. Squares = 1,845 / 100 = 18.45, rounded up to 19 squares.

Step 6. Bundles = 19 x 3 = 57 bundles of 3-tab shingles.

At $35 per bundle, the estimated shingle cost is 57 x $35 = $1,995.

Roof Pitch

Steeper roofs have more surface area per square foot of footprint. A 4/12 pitch adds about 5.4% to the footprint area, while a 12/12 pitch adds 41.4%. Always measure the actual pitch rather than guessing, because even a one-step error changes the material estimate by 3 to 5 percent.

Roof Complexity

A simple gable roof has two planes and wastes about 10% of material on starter courses, ridge caps and trimming. A hip roof adds hip caps and angled cuts that raise waste to 15%. A complex roof with valleys, dormers and multiple ridgelines can waste 20% or more.

Shingle Type

Standard 3-tab shingles are thinner and lighter, so 3 bundles cover one square. Architectural (dimensional) shingles are thicker and heavier, so most brands pack them at 4 bundles per square. Check the manufacturer label for the exact coverage per bundle.

Roof Penetrations

Chimneys, skylights, vents, and plumbing stacks interrupt the shingle field. Small penetrations (pipe boots, vents) are negligible, but a large skylight or chimney can reduce the shingle area by 10 to 30 square feet. This calculator does not deduct penetrations, so your actual material need may be slightly lower.

Underlayment and Ice Shield

This calculator estimates shingle bundles only. You also need roofing felt or synthetic underlayment for the entire roof area, plus ice and water shield along eaves in cold climates. Order underlayment to match the total area with waste.

For ordering the lumber to frame the roof structure, see the lumber calculator.

New Construction Estimate

Before framing begins, convert the architectural footprint and planned pitch into a shingle order. This gives a budget number for the roofing line item in the construction estimate.

Tear-off and Re-roof

Measure the existing building footprint and pitch to estimate the replacement shingle quantity. Add the higher waste factor if the existing roof has dormers, valleys or irregular planes.

Insurance Claim Documentation

After storm damage, calculate the affected roof area to support the material line in the insurance claim. Use the exact pitch and footprint dimensions from the property survey or a roof measurement report.

Comparing Bids

Run your own estimate to verify that a contractor bid includes the right number of squares. A bid that is significantly under the calculated quantity may be using thinner coverage or a lower waste allowance.

Material Cost Budgeting

Enter the current price per bundle from your supplier to get a total shingle cost. Compare 3-tab and architectural shingles to see the cost difference before choosing a product.

1. Using Footprint Area Instead of Roof Area

A 6/12 pitch roof has 11.8% more surface area than the footprint. Ordering materials based on the flat footprint area leaves you short by one or two squares on a typical house.

2. Underestimating Waste on Complex Roofs

A simple gable roof wastes about 10%, but adding just one valley or dormer can push waste to 15 to 20%. Use the moderate or complex setting to avoid a second trip to the supplier.

3. Wrong Bundle Count for Architectural Shingles

Architectural shingles are heavier and typically require 4 bundles per square, not 3. Ordering based on the 3-tab ratio of 3 bundles per square leaves you 25% short.

4. Forgetting Ridge and Hip Caps

Ridge caps and hip caps are cut from full shingles or sold as separate cap bundles. The waste allowance in this calculator accounts for cap material on simple and hip roofs, but verify with your supplier for very long ridgelines.

5. Not Measuring the Actual Pitch

Guessing the roof pitch can throw off the multiplier by 5 to 10%. Measure the rise over a 12-inch level run from the attic or use an inclinometer from the ground. For attic framing, see the ceiling joist span calculator.

This calculator gives a material-order estimate based on a rectangular footprint and a single uniform pitch. It does not model T-shaped or L-shaped buildings with different pitches on each wing.

For standard 3-tab shingles, you need 3 bundles per roofing square (100 sq ft). Architectural or dimensional shingles are heavier and typically require 4 bundles per square, though some brands vary. Check the coverage listed on the bundle wrapper.

A roofing square is a unit of measurement equal to 100 square feet of roof surface area. Roofers and suppliers quote prices and quantities in squares rather than individual square feet because it simplifies ordering and estimating.

From inside the attic, hold a level horizontally against a rafter and measure the vertical rise over 12 inches of horizontal run. A rise of 6 inches per 12 inches of run is a 6/12 pitch. You can also use a smartphone inclinometer app held against the roof surface.

Yes. A steeper pitch means more roof surface area per square foot of building footprint. A 12/12 pitch roof uses about 41% more shingles than a flat roof over the same footprint, because the pitch multiplier is 1.414 at 45 degrees.

Add 10% waste for a simple gable roof, 15% for a hip roof or one with moderate complexity, and 20% for a complex roof with dormers, valleys and multiple ridgelines. The waste covers starter strips, ridge caps, hip caps and cutting losses.

Most asphalt shingle manufacturers require a minimum pitch of 4/12 for standard installation. Roofs between 2/12 and 4/12 can use asphalt shingles with additional underlayment, but roofs below 2/12 typically need a low-slope membrane system.

Multiply the total number of bundles by the price per bundle. This gives the shingle material cost only. A complete roofing job also includes underlayment, flashing, nails, ridge vents and labor, which typically add 50 to 100% to the shingle cost alone.

This calculator estimates the roof area and pitch multiplier correctly for any roof type, but the bundle and square counts apply only to asphalt shingles. Metal roofing is sold in panels by the linear foot, so convert the roof area to panels using the panel width and coverage.

A gable roof has two sloping planes that meet at a ridge, with vertical triangular walls (gables) at each end. A hip roof has four sloping planes that meet at a ridge or a point, with no vertical gable walls. Hip roofs waste more material because of the angled hip cuts.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Remodel Calculators, Roofing Calculator (pitch multiplier method, waste factors and bundle counts for shingle estimation).
• Tall Yard, Roof Area Calculator (pitch multiplier table verified for pitches 1/12 through 16/12).
• CalcSummit, Roofing Calculator (3-tab vs architectural bundle-per-square counts, waste factor ranges).