Log Board Foot Calculator
Enter a log's small-end diameter and length to see its board feet by the three common log rules: Doyle, Scribner Decimal C and International 1/4-inch. Free, no sign-up.
Doyle 144 BF, Scribner Decimal C 160 BF, International 180 BF. Scaled as 16 in. × 16 ft.
Scaled as 16 in. × 16 ft.
Diameters 6–40 in., lengths 4–20 ft. Scale longer logs as two or more logs.
What log scale measures
A log rule estimates how many board feet of lumber a sawmill can cut from a log. Each rule starts from a different idea of the sawing, so the same log scales differently: a 16-inch, 16-foot log is 144 board feet by Doyle, 160 by Scribner Decimal C and 180 by the International 1/4-inch rule. That's log scale: an estimate made before sawing. The lumber you get is tallied board by board afterwards, as on the board foot calculator.
How to measure a log
- Diameter: inside the bark at the small end, in two directions at right angles (USDA Forest Service Log Scaling Handbook, ch. 10 §17.3).
- Round, then average. Read each diameter to the nearest inch (an exact half rounds up), then average the two. An average that lands on a half inch rounds down: readings of 24 and 25 inches scale as 24. Enter that average; the calculator rounds a typed diameter the same way.
- Length: the log's length in whole feet, after the trim allowance your contract or mill uses. A fraction of a foot is dropped: a hardwood log just short of a full foot is tallied at the next lower foot (Purdue FNR-191).
- Over 20 feet: scale it as two or more logs and add them (Freese 1973; the handbook's Appendix 1 lists the splits).
The calculator applies the same rounding, and says which sizes it scaled.
The three log rules
Doyle
Board feet = (D − 4)² × L ÷ 16
D is the small-end diameter in inches and L the length in feet (Purdue FNR-191; UT Extension PB 1650). Subtracting 4 inches allows for slabs and edgings, and log taper is ignored. Doyle is the most widely used rule on private timber in the East and South, and it scales small logs low.
Scribner Decimal C
Scribner is a diagram rule: J. M. Scribner drew the 1-inch boards that fit in circles of each diameter (Freese 1973). The Decimal C form rounds to the nearest 10 board feet and drops the zero, so a log of 136 to 145 board feet is written 14 (Log Scaling Handbook, ch. 10 §14). It's a table, not a formula. The calculator looks values up in the Forest Service table (Appendix 2). For a 19-foot log it takes the value halfway between 18 and 20 feet and rounds a half to the even value, as the handbook says for odd lengths.
International 1/4-inch
Each 4-ft section = (0.22D² − 0.71D) × 0.905
The rule assumes 1/2 inch of taper in every 4 feet, so each 4-foot section is figured at a diameter 1/2 inch larger than the one before, and the sections are added (Log Scaling Handbook, Appendix 8; Freese 1973). The 0.905 converts Clark's 1/8-inch saw kerf to 1/4 inch. The total rounds to the nearest 5 board feet. For a length that isn't a multiple of 4 feet, the calculator adds the leftover feet as a share of the next section. That matches the Forest Service table except in a handful of cells that print 5 board feet more and a few misprints. Where both published tables print the higher value (five cells), the calculator shows it.
Doyle, Scribner and International compared
Board feet in a 16-foot log, computed with the calculator's own maths:
| Small-end diameter | Doyle | Scribner Decimal C | International 1/4″ |
|---|---|---|---|
| 6″ | 4 | 20 | 20 |
| 8″ | 16 | 30 | 40 |
| 10″ | 36 | 60 | 65 |
| 12″ | 64 | 80 | 95 |
| 14″ | 100 | 110 | 135 |
| 16″ | 144 | 160 | 180 |
| 18″ | 196 | 210 | 230 |
| 20″ | 256 | 280 | 290 |
| 22″ | 324 | 330 | 355 |
| 24″ | 400 | 400 | 425 |
| 26″ | 484 | 500 | 500 |
| 28″ | 576 | 580 | 585 |
| 30″ | 676 | 660 | 675 |
| 32″ | 784 | 740 | 770 |
| 34″ | 900 | 800 | 875 |
| 36″ | 1,024 | 920 | 980 |
| 38″ | 1,156 | 1,070 | 1,095 |
| 40″ | 1,296 | 1,200 | 1,220 |
In 16-foot logs, Doyle gives the least of the three (or ties) up to 28 inches, and the most from 30 inches up. Which rule applies is a matter of local custom and the contract: Doyle, Scribner and International have each been the statute rule in different states (Freese 1973), and National Forest board-foot sales use Scribner Decimal C unless the contract names the International rule (36 CFR 223.36).
Log board foot FAQ
Which log rule should I use: Doyle, Scribner or International?
Use the one the buyer and seller agree on; a timber sale contract names it. Doyle is the most widely used rule on private timber in the East and South, and the International 1/4-inch rule is probably the most accurate of the three (Purdue FNR-191). National Forest timber sold by the board foot is scaled by Scribner Decimal C unless the contract names the International rule (36 CFR 223.36).
Why does the Doyle rule give so little for small logs?
Doyle takes 4 inches off the diameter for slabs and edgings before squaring it, which costs a small log a larger share of its volume (Purdue FNR-191). A 12-inch, 16-foot log scales 64 board feet by Doyle, 80 by Scribner Decimal C and 95 by the International 1/4-inch rule.
How do I measure a log's diameter for scaling?
Measure inside the bark at the small end of the log, in two directions at right angles. Read each to the nearest inch (an exact half rounds up) and average the two; an average on a half inch rounds down, so readings of 24 and 25 inches scale as 24 (USDA Forest Service Log Scaling Handbook).
How do I scale a log longer than 20 feet?
Scale it as two or more shorter logs and add them up. The International rule's author specified this for lengths over 20 feet (Freese 1973), and the Forest Service handbook lists how to divide long logs into segments of 20 feet or less (Appendix 1).
Sources
- USDA Forest Service. Forest Service Handbook 2409.11, National Forest Log Scaling Handbook. WO Amendment 2409.11-2006-1, effective October 30, 2006. Used: Ch. 10 §14 (Scribner Decimal C rounds to the nearest 10 BF; International 1/4-inch to the nearest 5 BF), §17.3 (diameter inside bark at the small end, two readings at right angles, each to the nearest inch, averaged; an average on a half inch rounds down), §17.15 (odd lengths interpolated, halves to even); Appendix 1 (long logs divided into segments); Appendix 2 (Scribner Decimal C table); Appendix 8 note 1 (V = (0.22D² − 0.71D) × 0.905 per 4-ft section, 1/2 in. taper per 4 ft).
- USDA Forest Service, Forest Products Laboratory. A Collection of Log Rules (General Technical Report FPL-1). 1973. Frank Freese. Used: Doyle, Scribner and International 1/4-inch entries: formulas, history, the states that made each a statute rule; International volumes accumulate 4-ft sections and lengths over 20 ft are scaled as two or more logs. Readable copy.
- Purdue University Cooperative Extension Service. Log and Tree Scaling Techniques (FNR-191). December 2001. Daniel L. Cassens. Used: Doyle formula (D − 4)² × L/16; International 1/4-inch length formulas; Tables 1–3; where each rule is used; diameter measured in two directions at right angles; a fraction of a foot dropped in hardwoods.
- University of Tennessee Extension. Understanding Log Scales and Log Rules (PB 1650). Revised February 2011. Brian Bond. Used: Doyle formula; Table 3 comparison of the three rules for 16-ft logs; which rule is used where.
- Code of Federal Regulations (eCFR). 36 CFR 223.36, Volume determination. Current text on eCFR, read October 26, 2026. Used: (b): National Forest timber sold by board feet is scaled by the Scribner Decimal C log rule unless the contract names an International 1/4-inch rule.