FREE · PRIVATE · INSTANT

Lumber Calculator

Lumber Calculator estimates stock boards, board courses, and board feet for decking, siding, or other rectangular board coverage. Enter job dimensions in U.S. customary units, adjust supplier assumptions, and get purchase-ready quantities instantly.

Loading calculator…

HOW IT WORKS

Formula and assumptions

Round whole board courses and stock lengths for the covered surface, then apply cutting waste and calculate purchased board feet.

Boards run along the entered covered length.
Actual board width, stock length, thickness, gaps, and waste are editable.

FIELD CHECK

Before you order

Enter actual board width, gap, stock length, thickness, and waste; cut optimization, defects, grade, moisture, and span requirements still need project data.

Worked example

Example: with covered length 20 ft, covered width 12 ft, matching surfaces 1, actual board width 5.5 in, the lumber calculator returns 63 boards for boards to buy. The supporting check is board courses: 27 courses. Replace the prefilled measurements and supplier assumptions with the project values before ordering.

PROJECT GUIDE

Using this calculator well

WHEN TO USE IT

Best use of this calculator

Use the result as a planning estimate, then verify field measurements and product-specific data before ordering or building.

INPUTS EXPLAINED

What each input means

Covered length: Enter the measured value and choose the matching unit (ft, in, yd, m, cm).
Covered width: Enter the measured value and choose the matching unit (ft, in, yd, m, cm).
Matching surfaces: Enter the project value used by the calculation.
Actual board width: Enter the measured value and choose the matching unit (in, ft, cm, mm).
Gap between boards: Enter the measured value and choose the matching unit (in, ft, cm, mm).
Stock board length: Enter the measured value and choose the matching unit (ft, in, yd, m, cm).
Actual board thickness: Enter the measured value and choose the matching unit (in, ft, cm, mm).
Cutting / defect waste: Enter the project value in %.
Price per board: Enter the project value in $.

COMMON MISTAKES

Checks that prevent bad estimates

Mixing units or entering a measurement in a different unit than the selected field unit.
Using a planning default when the exact manufacturer or supplier specification is available.
Rounding intermediate measurements too early instead of rounding the final purchase quantity.
Ignoring waste, compaction, cuts, laps, settlement, or full-package rounding where the project requires them.

SOURCES & REVIEW

How this estimate is supported

The implemented formula, assumptions, and worked example on this page are the calculator-specific reference. BuildYard's broader rules are documented in the Calculation Methodology and Sources & References.

For material density, coverage, yield, dimensions, package quantity, price, and other product-specific values, the current manufacturer or supplier specification should override a planning default.

Last reviewed: September 15, 2026, as part of the site-wide calculator workflow validation pass. See the BuildYard Changelog.

COMMON QUESTIONS

Lumber Calculator FAQ

What does the Lumber Calculator calculate?

It converts the measurements for decking, siding, or other rectangular board coverage into the buying units normally used for stock boards, board courses, and board feet, with the relevant waste, package, weight, or cost outputs shown on the result card.

How accurate is this lumber calculator?

The geometry is calculated from the values you enter. Final ordering accuracy still depends on field measurements, supplier density or coverage, product dimensions, compaction, cuts, and the selected allowance.

What should I verify for decking, siding, or other rectangular board coverage?

Enter actual board width, gap, stock length, thickness, and waste; cut optimization, defects, grade, moisture, and span requirements still need project data. Confirm the selected product, field conditions, and purchasing increments before placing the order.

Should I round the result up?

Yes for indivisible buying units such as bags, sheets, bundles, pallets, boxes, bars, and truck loads. The calculator rounds those purchase quantities up automatically.

KEEP ESTIMATING

Related framing calculators

All Framing tools

Framing