Wood & Trim
Lumber Calculator
Convert finished piece counts into stock lumber to buy.
Enter your measurements
Results update as you type.
About this calculator
Enter the nominal size, number of finished pieces, piece length, stock length and waste. The calculator uses NIST PS 20 actual dimensions, works out how many pieces fit per stock length and rounds the purchase up.
How to use this calculator
- Pick the nominal size from the list.
- Enter how many finished pieces you need and their length.
- Choose the stock length available at your yard.
- Allow for saw kerf explicitly, then add waste for defects and end trimming.
- Check the actual dimensions before planning joinery.
Formula
Pieces per stock = floor((stock length + kerf) ÷ (piece length + kerf))
Stock pieces = ceil(finished quantity × (1 + allowance/100) ÷ pieces per stock)
Assumptions
- Finished pieces are cut from straight, defect-free stock with one piece per cut.
- Waste is applied to the piece count, then the purchase rounds up.
- Actual dimensions follow NIST PS 20 dressed sizes.
Common mistakes
- Ignoring saw kerf when finished lengths exactly fill the stock.
- Treating a nominal size as its dressed dimension.
- Using a percentage allowance as a substitute for a feasible cutting layout.
Worked example
Try it: press “Load example” above the form.
Ten 2 ft pieces from 8 ft stock fit three pieces per stock after allowing 1/8 in saw kerf. With a 10% piece allowance, buy four stock lengths.
Limitations
No cut optimization, end trimming, defects, grain matching or structural design. Kerf is allowed between equal finished pieces only.
Frequently asked questions
Why do four 2 ft pieces not fit an 8 ft board?
Four finished pieces already use the entire 8 ft. Saw cuts remove extra material. With a 1/8 in kerf, the model fits three such pieces per 8 ft stock length unless extra stock length or a different cutting plan is available.
Does a 2×4 measure 2 by 4 inches?
Standard dry dressed 2×4 lumber is commonly 1.5 by 3.5 inches. Confirm the grade, moisture and finished dimensions of the actual stock. Nominal names are not structural suitability checks.
What does the worked example show?
Ten 2 ft pieces from 8 ft stock fit three pieces per stock after allowing 1/8 in saw kerf. With a 10% piece allowance, buy four stock lengths.
Which assumptions should I check before using the result?
No cut optimization, end trimming, defects, grain matching or structural design. Kerf is allowed between equal finished pieces only.
Sources
Sources explain the methods and any named product presets. Check your product label where coverage, yield or density differs.
- NIST: PS 20 American Softwood Lumber Standard
DOC PS 20-25, Table 3: nominal and minimum dressed sizes. Confirm moisture, grade, species and actual stock; this is not a fastener schedule, span or structural-design reference.
Calculation documentation · Updated 2026-11-08 · Version 1.6.4. Estimates are planning aids. Confirm quantities, coverage and prices with your supplier before purchasing. Found an error? Report it.
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