Roof Replacement Cost Calculator
Estimate a replacement roof from plan dimensions, pitch, waste, user-entered rates, tear-off, repairs, accessories, permits, tax, overhead and contingency.
Example values are ready. Select Calculate.
All prices are your entries; the calculator does not infer regional bids. Currency selection changes formatting only. Tax is applied only to roofing material, underlayment, flashing, ventilation and gutters. Confirm local tax treatment and contractor scope.
How the roof replacement estimate works
Measure the horizontal roof plan, including overhangs. Enter the rise for every 12 inches of horizontal run. The calculator converts the plan area to sloped area, adds the selected waste allowance and applies only the rates and fixed amounts you enter. Divide complex roofs into non-overlapping rectangles and add their plan areas before using this single-section model.
Formulas
Slope factor = √(1 + (pitch ÷ 12)²). Sloped roof area = plan length × plan width × slope factor. Purchase area = sloped area × (1 + waste%). Decking repair area = sloped area × repair%. Each area-based cost equals its applicable area multiplied by the entered rate. Tax is applied to the entered material items identified above. Overhead is applied after tax; contingency is applied to that base.
Worked example
A 40 × 30 ft plan with a 6:12 pitch has a slope factor of 1.1180 and a sloped area of 1,341.64 ft². With 12% waste, the purchase area is 1,502.64 ft² or 15.026 roofing squares. Using the example rates and allowances above produces a $10,860.72 subtotal before tax, $564.31 tax, $1,713.76 overhead, a $13,138.79 base and $1,313.88 contingency, for an estimated total of $14,452.67.
What is included and excluded
The estimate can include roofing material, tear-off, disposal, underlayment, a percentage of decking replacement, flashing, ventilation, gutters, permits, other entered costs, tax, overhead and contingency. It does not infer structural repairs, multiple roof sections, valleys, dormers, chimneys, solar removal, hazardous materials, code upgrades, access constraints, weather protection, regional prices or contractor availability. Use written quotes and local requirements for a real project.
Frequently asked questions
Is a roofing square the same as a square foot?
No. One roofing square is 100 square feet of roof covering. The calculator reports purchase squares after the waste allowance.
Should tear-off use purchase area?
This calculator applies tear-off to the existing sloped roof area and material plus underlayment to the purchase area. That avoids charging removal for new waste material.
What should I enter for decking repairs?
Enter the share of sloped area you reasonably expect to replace and a rate per square foot or square meter. Set the percentage or rate to zero if decking is excluded or unknown.
Does changing currency convert exchange rates?
No. Currency selection only formats the values. All entered rates and allowances must already use the chosen currency.
Related calculators
- Roofing Calculator — estimate sloped area, squares and bundles.
- Roof Pitch Calculator — convert rise, angle and slope.
- Home Addition Cost Calculator — build an itemized addition budget.
- Home Maintenance Calculator — plan ongoing ownership reserves.