How do the three log rules differ?
- Doyle — simple and widely used in the eastern US; it tends to under-estimate small logs and over-estimate large ones.
- Scribner (approximation) — a mathematical curve approximating the Scribner diagram rule. It is not the exact Scribner table nor Scribner Decimal C, so it can differ from a printed Scribner tally.
- International 1/4-inch — generally the closest estimate of sawn yield; built from 4-foot sections with an allowance for saw kerf and taper.
The three results are shown separately on purpose. Averaging them would invent a number that no rule actually produces, and the spread between them is itself the useful information.
Which diameter and length do I enter?
- Diameter: across the small end of the log, inside the bark, in whole inches.
- Length: the nominal log length — the length it is sold or bucked at, not a tape reading to the inch.
- Both are picked from lists rather than typed, because log rules are only defined at these nominal sizes.
How are the numbers rounded?
Doyle and Scribner keep full internal precision and are displayed to one decimal; totals add the unrounded values first, so a total never drifts from its parts. International values are rounded to the nearest 5 board feet per log (ties rounded up), following University of Tennessee PB1650, and the rounded values are then summed.
Log board foot vs board foot — which one?
Use this calculator while the wood is still a round log and you want an estimate of what it will yield. Once the log is sawn and you can measure a board's thickness, width and length, switch to the Board Foot Calculator — that one is exact arithmetic on real dimensions, not an estimate of yield.
Frequently asked questions
What diameter do I measure?
The diameter across the small end of the log, measured inside the bark, in whole inches. This is the standard input for log scaling rules.
Why do the three methods give different board feet?
Each rule was derived differently — a formula, a diagram, or a sectional model — so they disagree, especially on small logs. Comparing them shows the range you might expect.
Is this the exact Scribner scale?
No. The Scribner column is a mathematical approximation of the Scribner rule, not the official Scribner table or Scribner Decimal C. Use it as an estimate.
Can I enter metric measurements?
Diameter and length are chosen from nominal US sizes because log rules are defined in inches and feet. Metric mode shows the exact millimetre and metre equivalents of those same nominal sizes.
Will I actually get this much lumber?
Not exactly. These are estimates. Real recovery depends on defects, taper, sawing method and kerf.
Sources
- University of Tennessee Extension, PB1650 — International 1/4-inch coefficients and the nearest-5-board-foot rounding (pp. 3–4).
- Doyle and Scribner rule formulas as commonly published for log scaling.