How much lumber is really in that log? Enter the small-end diameter (inside bark) and log length — this log scale calculator returns all three classic log rules side by side, because the answer honestly depends on which rule the deal is written in.
Doyle (1825) — BF = ((D − 4) ÷ 4)² × L. That fixed 4-inch slab allowance is brutal on small logs, which is exactly why mills like buying on Doyle: an 8″ × 8′ log scales just 8 board feet on Doyle but around 20 on International ¼″. The gap narrows as diameter grows and flips past ~28″.
Scribner (1846) — drawn from diagrams of 1-inch boards fitted inside circles of each diameter, then published as tables. This calculator uses the standard decimal approximation (0.79·D² − 2D − 4) × L ÷ 16, which tracks the printed Scribner Decimal C tables within a few board feet on common log sizes.
International ¼″ (1906) — computed in 4-foot sections with ½″ of taper per section and a ¼″ saw kerf. It is the only rule built from how saws actually eat a log, and modern yield studies keep confirming it: if you want to know what a band mill will really recover, read the International column.
Yield reality check: all three rules assume a sound, straight log. Sweep, rot, shake and big knots come off the top — a seasoned scaler may deduct 10–30% before applying the rule. If you are milling your own lumber with a chainsaw mill, expect closer to the Doyle figure: wider kerf, fewer salvageable side boards.
Formulas & worked values cross-checked against Purdue extension FNR-191 and Penn State Extension log-scaling tables. Our 16″ × 12′ example: Doyle 108 · Scribner ≈125 (printed table 128) · International ¼″ ≈130.
Small end, inside the bark. Out-of-round log? Average two readings taken at right angles.
Whichever the buyer scales with — ask before the log leaves the landing. Eastern hardwood markets usually run Doyle; many state and federal timber sales specify International ¼″.
Between Doyle and Scribner for most chainsaw-mill setups. Thick kerf and simple cant sawing cost you the side boards the International rule counts on.
Scaling starts at the small end: measure the diameter inside the bark; if the end is oval, take the narrow and wide readings and average them, rounding down to the nearest inch. Length is measured to the last full foot (a 12′7″ log scales as 12′), and honest scaling leaves 3–4″ of trim allowance beyond the plan so end checks can be cut away. Deduct before you dream: sweep over 2″ per 8 feet, visible rot, ring shake and a big catface all come off the scale — a seasoned buyer will knock 10–30% for defect, so a self-scaled "150 bf log" and a mill's "110 bf log" are often the same log. The worked method matches Purdue Extension's FNR-191 log-scaling guide, the reference this page's numbers are checked against.
| Small-end Ø × 12′ | Doyle | Scribner | Int'l ¼″ | Doyle gap |
|---|---|---|---|---|
| 12″ | 48 | 64 | 69 | −30% |
| 16″ | 108 | 125 | 131 | −18% |
| 20″ | 192 | 204 | 212 | −9% |
| 24″ | 300 | 302 | 311 | −4% |
The pattern is the whole negotiation: Doyle's fixed 4-inch slab allowance punishes small logs hard and fades as diameter grows. Selling 12–16″ hardwood on Doyle leaves real board feet on the table; by 24″ the three rules nearly agree. That asymmetry — not arithmetic — is why "which rule?" is the first question of any log deal.