Roofing Calculator

1. 1Calculate the roof surface area from dimensions and pitch, or enter the roof area or roofing squares you already have.
2. 2Convert the area to roofing squares: 1 roofing square = 100 sq ft.
3. 3Add the extra material allowance you want to plan for.
4. 4Use the bundle coverage printed on the shingle product you plan to buy.
5. 5Calculate starter, hip & ridge and underlayment separately, each from its own product coverage.
6. 6Add drip edge, ice & water barrier, fasteners and cost only if you need them.

Quick Estimate stops at roof area, squares and field-shingle bundles. Detailed Estimate adds starter, hip & ridge, underlayment, ice & water barrier, drip edge, fasteners, tear-off reference and optional cost.

One roofing square equals 100 square feet of roof area — the standard measure used across the roofing trade.

A square measures area; a bundle is packaging. The number of bundles in a square depends on the product.

Roof area is larger than the building footprint whenever the roof is pitched, because the sloped surface is longer than the horizontal run. This calculator applies the pitch multiplier from the same shared roof engine used across the roofing cluster, so the numbers agree exactly.

Three bundles per square is common for many asphalt products, but specialty and heavier shingles can differ — some use four or five bundles per square. Use the actual package or manufacturer coverage.

Both calculators share the same shingle engine, so the bundle counts match for identical inputs.

Once you have quantities, the Roof Cost Calculator applies your own material, labor, tear-off, disposal, decking, permit and delivery prices to them and reports a project total with cost per square foot and per roofing square. It never recalculates quantities — it only prices the ones these roofing pages produce.

Starter products are measured by linear edge coverage, and coverage differs by product. Choose whether you are planning starter at eaves, rakes or both — nothing is assumed.

Follow the manufacturer's installation instructions for where starter is used and how it is fastened.

Cap quantities come from total hip and ridge length with the cap product's own linear coverage. Cap coverage is never inferred from field shingles.

A shed roof usually has no ridge line, so the section can simply be switched off — disabled categories never appear in the results or totals.

Underlayment is measured by roof area and roll coverage. Roll size and effective coverage vary, so the product's stated coverage is the source of truth, and the allowance is separate from the shingle allowance.

Drip edge is ordered as stock pieces, so the selected edge lengths are adjusted for overlaps and cuts, then divided by the stock piece length you are buying.

Flashing quantities depend on wall intersections, chimneys, valleys, skylights and penetrations, so they are not estimated automatically. Use the other-materials cost field for those items.

Roof ventilation is not calculated here. Ventilation requirements cannot be determined from roof square footage alone.

Extra material may be needed for several reasons:

• Cuts
• Hips
• Valleys
• Dormers
• Starter layouts
• Damaged material

The appropriate allowance depends on roof geometry and the roofing product, so BuildCalcWorks keeps it a choice. No single percentage is correct for every roof, and complex valleys, hips and dormers usually mean more cutting.

Actual roof area and material planning area are always reported separately, so geometry is never replaced by waste-adjusted values.

The optional tear-off section calculates the coverage of existing roofing layers for planning purposes.

Tear-off coverage is a planning reference only. It does not determine disposal weight, container size, or whether existing roofing layers may remain — those depend on the product, local code and the roof itself.

Field shingle bundles, starter bundles, ridge-cap bundles and underlayment roll coverage all vary by manufacturer and product line, so none of them is hidden inside a constant here — every coverage value is visible and editable.

For best accuracy, use the exact coverage information printed on the shingle, starter, ridge-cap and underlayment products you plan to purchase.

Roof work and direct roof measurement can involve fall hazards. Use plans, safe measurement methods, or qualified professionals where appropriate.

Roof measurement and roofing work may involve serious fall hazards. Use building plans, safe ground-based or aerial measurement methods, or qualified professionals where appropriate.

This calculator estimates roofing materials from dimensions and product coverage values. It does not evaluate roof structure, decking condition, structural loads, ventilation design, code compliance, permitted roofing materials, whether reroofing over existing layers is allowed, safe roof access or installation suitability.

Labor, tear-off labor, disposal, decking repairs, flashing replacement, ventilation and permits are not part of the material estimate.

How BuildCalcWorks calculations are created →