Scribner Log Rule
The Scribner log rule (1846) is a diagram-based scale that visualizes how many rectangular boards fit inside a circular log end. Its Decimal C variant remains the required scale for federal timber in the US Pacific Northwest.
Scribner is a diagram rule ā it doesn't have one clean algebraic formula. The calculator below uses a widely accepted polynomial approximation matching the published Scribner table for 16-ft logs, then scales linearly for other lengths.
How Scribner Works
Rather than a single formula, Scribner is built by drawing all the 1-inch-thick boards that fit inside a circular log cross-section, subtracting a fixed Ā¼-inch kerf between boards, and summing the total board area. The scale ignores taper ā it treats the whole log as a cylinder with the small-end diameter.
Approximate formula
BF ā (0.79 DĀ² ā 2 D ā 4) Ć (L Ć· 16)
Reasonable for D between 12 and 40 inches, L between 8 and 20 feet. Smaller logs use published table values.
Scribner Decimal C
The "Decimal C" variant rounds Scribner values to the nearest 10 BF and drops the trailing zero. So a 176 BF Scribner value becomes "18" on a Decimal C tally sheet. This saves ink on paper ledgers ā a big deal when the rule was standardized in the 1800s.
- Full Scribner: 176 BF
- Decimal C: 18 (= 180 BF, rounded)
Scribner BF Table
| SED (in) | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft | 18 ft | 20 ft |
|---|---|---|---|---|---|---|---|
| 8 | 20 | 25 | 30 | 35 | 40 | 45 | 50 |
| 10 | 28 | 35 | 42 | 48 | 55 | 62 | 68 |
| 12 | 42 | 52 | 63 | 73 | 85 | 95 | 106 |
| 14 | 60 | 75 | 90 | 105 | 120 | 135 | 150 |
| 16 | 82 | 103 | 124 | 145 | 166 | 186 | 207 |
| 18 | 108 | 135 | 162 | 188 | 215 | 242 | 269 |
| 20 | 140 | 175 | 210 | 245 | 280 | 315 | 350 |
| 24 | 215 | 268 | 322 | 375 | 430 | 484 | 537 |
| 28 | 301 | 376 | 451 | 527 | 602 | 677 | 752 |
| 32 | 400 | 500 | 600 | 700 | 800 | 900 | 1,000 |
Where Scribner Is Standard
US Federal Timber (Pacific Northwest)
The US Forest Service and Bureau of Land Management require Scribner Decimal C for timber-sale cruises and mill tally in Oregon, Washington, and parts of California and Idaho. If you're bidding on federal timber in the PNW, expect Scribner numbers throughout the paperwork.
State timber agencies
Most western states (WA DNR, OR DOF, MT DNRC) also use Scribner. It's the default scale in almost every log-yard system in the region.
Private industrial mills
PNW mills convert Scribner-purchased logs to lumber but usually invoice customers in per-piece or per-MBF standard measure. The scale exists mostly at the buying end of the supply chain.
Where Scribner is not used
- Midwest/South US: Doyle dominates
- Northeast US, Appalachia: International Ā¼-inch
- Canada: mostly metric cubic meters
Scribner FAQ
What is Scribner Decimal C?
Scribner values rounded to the nearest 10 BF, with the trailing zero dropped. 176 ā 18 (meaning 180 BF). Standard tally format for US Forest Service.
Why does Scribner ignore taper?
Historical simplicity. When the rule was published in 1846, portable computing meant a pencil ā a diagram based only on small-end diameter was practical for field scaling.
Is Scribner accurate?
Reasonably ā closer to actual sawn yield than Doyle, but still 5ā15% low compared to International Ā¼-inch on modern band mills.
What kerf does Scribner assume?
Ā¼-inch, matching a typical circular-saw mill from the mid-1800s. Modern band mills have thinner kerf and produce measurable overrun.
Can I convert Scribner to International?
Approximately: multiply Scribner by 1.05ā1.15 for typical logs. Larger multiplier for small logs, smaller for large.
Who was Scribner?
J.M. Scribner published the diagram-based scale in "Ready Reckoner" in 1846. The rule was later refined and standardized as "Scribner Decimal C" in the early 1900s.