Free estimate — verify against local code before building
Roofing Calculator
See exact gable geometry, every allowance, and each whole package behind the roofing order.
What this calculator includes
Estimate one simple gable roof from its footprint, pitch, equal overhang, and waste allowance. The result separates exact roof area from shingle order area, package rounding, low-slope underlayment layers, and per-edge drip-edge stock. Edit product coverage and prices to match the labels you will buy. This is not a roof loading, sheathing, attachment, flashing, ventilation, wind, or structural design.
How to use this roofing calculator
- 01
Measure the simple gable footprint
Enter building length and width plus equal eave/rake overhang. Measure hips, valleys, dormers, walls and intersecting roof sections separately rather than forcing them into this gable model.
- 02
Enter pitch and waste
Pitch is rise per 12 inches of horizontal run. The calculator applies the geometric slope factor, then applies waste separately so exact area and order area remain visible.
- 03
Match the product labels
Open advanced assumptions and enter bundles per square, effective underlayment coverage, nail package size, accessory coverage, ice-barrier band, and current prices from the exact products selected.
- 04
Complete roof and safety review
Have the building official, roofer, designer or engineer verify roof loading and deck condition, approved covering and slope, wind classification, underlayment, ice barrier, flashing, ventilation, attachment, fire classification, reroofing limits, fall protection and permits.
Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- 2024 International Residential Code, Chapter 9 - Roof Assemblies (opens in a new tab)
Roof-covering scope, asphalt-shingle slope, underlayment, ice barrier, fastening, flashing and drip-edge provisions; local adoption controls.
- Asphalt Roofing Manufacturers Association - Technical Bulletins (opens in a new tab)
Industry application, storage, ventilation and asphalt-roofing guidance; the selected product instructions control package coverage and installation.
- OSHA Residential Fall Protection (opens in a new tab)
Construction fall-hazard requirements and guidance for residential work.
Frequently asked questions
How does pitch change roof area?
The calculator multiplies horizontal plan area by sqrt(12 squared plus rise squared), divided by 12. A 6:12 pitch has a factor of about 1.118. This geometric conversion does not evaluate structural roof loads.
Why is drip edge rounded on each side?
Stock must cover two eaves and two rakes, and adjacent segments overlap. The estimate rounds each edge independently instead of assuming every offcut can turn a corner, then shows purchased and leftover linear feet.
What happens between 2:12 and 4:12?
The estimate plans two underlayment layers for asphalt shingles in that slope range. Confirm the locally adopted code and approved shingle and underlayment instructions. Below 2:12, this asphalt-shingle calculator withholds the order.
Does the ice-barrier quantity prove code compliance?
No. The entered band width is a shopping assumption. Required coverage is measured relative to the exterior wall line and depends on slope, overhang, climate designation, assembly, adopted code and permitted exceptions.