Lumber Calculator
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Introduction
A repeated cut list becomes a purchase estimate only after each finished piece is fitted onto the stock length sold by the supplier. A 3.6-metre board may yield four 850-millimetre pieces, but a slightly longer cut or wider saw kerf can reduce that yield to three and increase the order by several boards.
Finished material and purchased material are different quantities. Finished volume is the wood that remains in the project. Purchase volume also contains offcuts, sawdust, allowance for defects or mistakes, and any extra boards caused by supplier bundle sizes. These additions occur at different stages, so combining them into one vague waste percentage can hide why the order increased.
Board width and thickness affect volume and price, but they do not change how many equal-length pieces fit along a board. Nominal names such as 2 × 4 are trade labels and may not equal the measured dimensions after drying and surfacing. Use the dimensions and price basis on the supplier quote, especially when comparing cubic-metre, board-foot, and per-board prices.
| Factor | Effect on the estimate |
|---|---|
| Cut length and kerf | Determine equal pieces per stock board |
| Piece count | Determines the minimum whole-board count |
| Waste allowance | Adds whole boards after the minimum count |
| Bundle size | Rounds the allowance count to the supplier's selling multiple |
| Dimensions and price basis | Convert the purchase count into volume and cost |
A repeated-cut estimate does not optimize a mixed cut list. It also cannot grade boards, place defects, follow grain direction, reserve reusable offcuts across jobs, or decide whether nominal dimensions are suitable. Those decisions still require a real cut layout and inspection before purchase.
How to Use This Tool:
Estimate one repeated finished length at a time and match every dimension to the stock that can actually be bought.
- Choose a Board size preset or enter measured thickness and width for custom stock.
- Enter the number of finished pieces, finished cut length, stock board length, and saw kerf with their correct units.
- Set a project-specific waste allowance and the supplier bundle size. Bundle rounding happens after the allowance is added.
- Select the supplier's price basis and enter the matching rate, then add tax or fees when they belong in the estimate.
- Check Pieces per stock board, Boards to buy, and Leftover per full stock board. Recalculate separately for another cut length or stock size.
Interpreting Results:
Base boards is the minimum whole-board count for the repeated cuts. Allowance boards includes the waste percentage, and Boards to buy includes final bundle rounding. The material allocation separates finished volume, cut loss and offcut, and extra purchase volume.
A sudden jump in quantity usually comes from an integer boundary. A few millimetres of kerf can reduce pieces per board, one extra base board can trigger a rounded waste board, and one allowance board can force purchase of a full supplier bundle.
Technical Details:
Lengths are converted to metres before yield, volume, and cost are calculated. Equal-cut yield counts a kerf only between adjacent finished pieces, which is why one kerf is added to both the stock-length numerator and cut-length denominator.
Formula Core
The purchase count is built through three upward-rounding stages: physical yield, waste allowance, and supplier bundle size.
Here, Ls is stock length, Lc is finished cut length, k is kerf, y is pieces per stock board, p is the required piece count, b is base boards, w is waste percent, a is allowance boards, g is bundle size, and q is boards to buy. All board counts are whole numbers.
Purchase volume is thickness × width × stock length × q. Board feet are found by dividing cubic metres by 0.002359737216. Subtotal cost uses one of three bases: purchase cubic metres × rate, purchase board feet × rate, or boards to buy × per-board rate. Tax or fees are then added as a percentage of the subtotal.
| Stage | Rounding or conversion | Why it matters |
|---|---|---|
| Yield | Floor to whole pieces per board | A partial piece cannot count |
| Base quantity | Ceiling to whole boards | All requested pieces must fit |
| Allowance | Ceiling after adding 0% to 40% | A fraction of a board becomes another board |
| Bundle | Ceiling to a multiple from 1 to 1,000 boards | The supplier may not sell individual boards |
| Price | Full precision until display | Quantity and tax use unrounded volume |
Limitations:
This is an equal-length takeoff, not a cutting-stock optimizer. Its offcut figure is geometric leftover from the modeled boards, not a promise that every remainder is reusable.
- Run separate estimates for materially different cut lengths or stock sizes.
- Inspect actual stock for defects, moisture, straightness, grade, and usable dimensions.
- Check the supplier's nominal-versus-actual size and pricing convention before comparing quotes.
Worked Examples:
Twenty-four repeated metric cuts
A 3.6 m stock board yields four 850 mm pieces when kerf is zero. Twenty-four pieces need six base boards. A 10% allowance rounds 6.6 up to seven boards, and a bundle size of one leaves the purchase count at seven. With 38 × 140 mm stock priced at 900 per cubic metre and no tax, the accepted estimate is 120.6576 before display rounding.
References:
- 7 CFR 1217.4 — Board foot, Legal Information Institute.
- Voluntary Product Standard PS 20-20: American Softwood Lumber Standard, National Institute of Standards and Technology, 2020.
- Making Sure that Lumber Measures Up, National Institute of Standards and Technology, March 1, 2017.