Commercial Roofing Calculator
Estimate a low-slope commercial roof in minutes: enter the measured deck area and roof system to get roofing squares, membrane rolls or sheets, polyiso insulation boards, and field fasteners — free, no signup.
How does a commercial roofing estimate work?
Commercial roofs are quoted and priced per square — one square is 100 sq ft of membrane surface, the same unit shingle jobs use. The difference is the system: low-slope roofs run TPO, PVC, EPDM, modified bitumen, or built-up roofing instead of asphalt shingles. Enter your measured deck area, pick the system, and this calculator returns orderable squares with a waste factor, membrane purchase units, and the insulation and fasteners to match.
The measured low-slope deck area — from a satellite takeoff or your site survey.
Parapets, penetrations, and seams drive 5–15% for low-slope work. Typical: 10%.
Roofing Squares
100.0 SQ
Order (waste)
110.0 SQ
Membrane rolls
11
Insulation Boards
344
Field fasteners and plates land at about 688 for a 100-square roof (4′ × 4′ grid). Confirm roll sizes and fastener schedules with your membrane supplier before ordering.
This result is free — the next steps are for pros
Why the waste factor and system matter
Parapets, penetrations, curbs, and seams force membrane to be cut and flashed — plan for 5% waste on clean rectangular decks and up to 15% on cut-up roofs with many penetrations. Your system changes the arithmetic too: TPO and PVC ship in 10 ft × 100 ft rolls (1,000 sq ft), EPDM in larger sheets, and modified bitumen and built-up roofing in much smaller rolls per square.
This estimator applies the same unit math a distributor runs: waste first, then divide by the system's coverage per roll or sheet, then round up. Insulation boards are sized at 4 ft × 8 ft (32 sq ft) per layer, and field fasteners assume a standard 4 ft × 4 ft mechanical-attachment grid — confirm both with your supplier, since wind codes and R-value targets change the schedule.
What else you'll need for the estimate
- Sloped or steep commercial? Use the pitch multiplier calculator to convert footprint to surface area first.
- Residential asphalt work instead? The shingle waste calculator handles bundles, underlayment, and ridge cap.
- Selling the job to the building owner? Show the payback with the roof replacement ROI estimator.
Browse all free roofing tools or start a full RoofHQ estimate to turn a measurement into a complete proposal.
Stop calculating by hand. Automate every estimate.
RoofHQ runs these numbers — plus full material orders, branded proposals, and deposits — automatically from one address.