Exterior calculator

Roof Sheathing Calculator

Estimate roof panel count from plan area, slope factor, and net sheet coverage. Switch between US customary and metric units, adjust the assumptions, and keep every step visible.

01 Measure02 Allow03 Order

Project inputs

Use one unit system throughout. Defaults show a realistic example; replace them with measurements from your project.

Unit system

Roof plan lengthPlanning default — verify the selected product or project specification.ftRoof plan widthPlanning default — verify the selected product or project specification.ftSlope factorPlanning default — verify the selected product or project specification.×Net coverage per sheetPlanning default — verify the selected product or project specification.ft²Waste allowanceEditable planning allowance for cuts, breakage, compaction, or site loss.%Price per sheetOptional local price; enter zero to hide the cost estimate.currencyCurrencyPlanning default — verify the selected product or project specification.

Measurement guideRun is horizontal. Rise is vertical. Measure the building length separately.

Measure the finished shape. Quantity only. Panel rating, thickness, orientation, edge support, clips, fastening, and loads require approved design and panel marks.

Estimate matches the inputs shown.

ReviewedNovember 2, 2026

ByBuildGauge Editorial Team

ScopeFormula, defaults & sources

Report an issue ↗

The calculation

A visible formula, not a black box.

Area & sheets · Mathematical derivationsheets = plan area × slope factor × waste factor ÷ net sheet coverage

Inputs are converted to a common base unit before calculation. Purchase quantities are rounded only at the final buying boundary.

Example inputDefaultStatus

Roof plan length40 ftPlanning default — verify

Roof plan width28 ftPlanning default — verify

Slope factor1.118 ×Planning default — verify

Net coverage per sheet32 ft²Planning default — verify

Waste allowance10 %Planning default — verify

Price per sheet38 currencyPlanning default — verify

CurrencyUSD Planning default — verify

Worked example

Example: planning roof sheathing

Using the editable example inputs—roof plan length 40 ft, roof plan width 28 ft, slope factor 1.118 ×—the calculator returns 44 sheets. Replace every example with measured dimensions and the selected product label before purchase.

Use this to understand the workflow—not as a recommendation for your project.

Sources & scope

What supports this calculation.

Industry guidanceAPA roof systems guidance ↗

Supports the product rule or estimating basis used by the Roof Sheathing Calculator; geometry and unit conversion remain visibly derived in the calculator.

Mathematical derivationNIST SI conversion factors ↗

Exact length, area, and volume unit conversions; the project formula is derived from standard geometry.

Common mistakes

Check the job, not just the number.

01Leaving the example roof sheathing inputs unchanged instead of entering measured project values.
02Treating an editable coverage, size, density, or allowance as universal instead of checking the selected product label, project documents, and local requirements.
03Ordering from the rounded result without reviewing exclusions: Quantity only. Panel rating, thickness, orientation, edge support, clips, fastening, and loads require approved design and panel marks.

Questions, answered

Roof sheathing FAQ

What does the Roof Sheathing Calculator estimate?

Estimate roof panel count from plan area, slope factor, and net sheet coverage. The primary output is area & sheets, with the intermediate assumptions kept visible.

How is the roof sheathing result calculated?

The visible formula is: sheets = plan area × slope factor × waste factor ÷ net sheet coverage. Inputs are converted to a common base unit before the final purchase boundary is rounded.

Are the default values recommendations?

No. Dimensions are worked examples and product-dependent presets are planning defaults. Replace them with the selected product label, project documents, and local requirements.

Is the result ready to order from?

Use it as a checked planning estimate, then confirm packaging, minimum orders, installation instructions, site conditions, and any code or professional-design requirements.