Log Board Foot Calculator (Doyle, Scribner and International Rules)

Sawlogs are bought and sold by the board foot, but nobody can know how much lumber a log holds until it is sawn. Log rules estimate it from the small-end diameter and the length, and the three common ones give quite different answers for the same log. This calculator works out all three, the Doyle, Scribner Decimal C and International 1/4 inch rules, using the formulas in the University of Tennessee Extension’s guide to log scales. Use it to check a mill’s scale, to compare prices quoted under different rules, or to estimate what your own logs will yield on a portable mill.

Log board feet calculator

How it works

D is the diameter inside the bark at the small end, to the nearest inch; L is the log length in feet:

Doyle: board feet = (D − 4)² × L ÷ 16. No allowance for taper. Too generous a slab allowance for small logs, too small for large ones.
Scribner: the original rule is a table drawn from sawing diagrams with a 1/4 in kerf. The guide gives a formula that closely estimates it, (0.79D² − 2D − 4) × L ÷ 16, and the Decimal C version rounds to the nearest 10 board feet.
International 1/4 inch: built up in 4 ft sections with 1/2 in of taper per 4 ft. For a 16 ft log, 0.796D² − 1.375D − 1.23, rounded to the nearest 5 board feet.

For International, the calculator uses one polynomial in L and D that reproduces the guide’s equations for 4, 8, 12, 16 and 20 ft logs (each 4 ft section adds 0.199D² − 0.642D, the guide’s 4 ft equation, with D growing 1/2 in per section; our tests check all five lengths), so lengths such as 10 or 14 ft are handled the same way.

Worked example

A 16 ft log, 16 in across the small end inside the bark:

Small-end diameter inside the bark: 16 in
Log length: 16 ft
Number of logs this size: 1
Log rule your buyer uses: Doyle

The calculator gives:

Doyle rule: 144 board feet
Doyle: 144 bd ft
Scribner Decimal C (formula): 170 bd ft
International 1/4 inch: 180 bd ft
Doyle as a share of International: 80%

Doyle gives 144 board feet, International 180 and the Scribner formula 170. The Tennessee guide’s table shows 144, 159 and 180 for this log, so Doyle and International match exactly and the Scribner formula runs about 10 board feet over the Scribner table here. Doyle is 80% of International for this log; for a 10 in log it is only 55%, which is why Doyle-scaled small logs are paid for at a higher price per thousand.

Board feet in a 16 ft log by each rule

Small-end diameter	Doyle	Scribner Decimal C (formula)	International 1/4 in
8 in	16	30	40
10 in	36	60	65
12 in	64	90	95
14 in	100	120	135
16 in	144	170	180
18 in	196	220	230
20 in	256	270	290
22 in	324	330	355
24 in	400	400	425
26 in	484	480	500
28 in	576	560	585
30 in	676	650	675

Computed from the formulas above. The Tennessee guide’s Table 3 (16 ft logs) gives Doyle 16, 36, 64, 100, 144, 256 and Scribner 32, 50, 79, 114, 159, 280 for 8 to 16 and 20 in logs, so the Scribner formula here can differ from the Scribner table by about 10 board feet.

International 1/4 inch rule by log length (board feet)

Small-end diameter	8 ft	10 ft	12 ft	14 ft	16 ft
8 in	15	20	25	35	40
10 in	30	35	45	55	65
12 in	45	55	70	85	95
14 in	65	80	100	115	135
16 in	85	105	130	155	180
18 in	110	140	170	200	230
20 in	135	175	210	250	290
22 in	170	215	260	305	355
24 in	205	255	310	365	425
26 in	240	305	370	435	500
28 in	280	355	430	505	585
30 in	325	410	495	585	675

Rounded to the nearest 5 board feet, as the rule is applied.

Doyle rule by log length (board feet)

Small-end diameter	8 ft	10 ft	12 ft	14 ft	16 ft
8 in	8	10	12	14	16
10 in	18	23	27	32	36
12 in	32	40	48	56	64
14 in	50	63	75	88	100
16 in	72	90	108	126	144
18 in	98	123	147	172	196
20 in	128	160	192	224	256
22 in	162	203	243	284	324
24 in	200	250	300	350	400
26 in	242	303	363	424	484
28 in	288	360	432	504	576
30 in	338	423	507	592	676

(D − 4)² × L ÷ 16.

Notes and limits

Measure inside the bark, across the small end. If the end is oval, measure the long and short axes and average them. Logs are tallied to the nearest inch: 12-1/4 in counts as 12, 12-3/4 as 13.
These are gross scale. Rot, splits, sweep and crook are deducted to get the net scale that the log is actually paid on.
The rule is mostly a matter of local custom. The Tennessee guide calls International 1/4 inch the most accurate of the three and Doyle the least, and says buyer and seller should agree on the rule before agreeing on a price.
The guide’s price conversions: multiply a Doyle price by 0.75 for Scribner and by 0.62 for International.
Once the logs are sawn, count the boards with the board foot calculator; for species properties see the wood species database.

Frequently asked questions

How many board feet are in a log?

It depends on the log rule. A 16 ft log 16 in across the small end is 144 board feet by Doyle, about 160 to 170 by Scribner and 180 by International 1/4 inch.

What is the Doyle log rule formula?

Board feet = (small-end diameter in inches − 4)² × length in feet ÷ 16. A 12 in by 16 ft log is (12 − 4)² × 16 ÷ 16 = 64 board feet.

Which log rule is most accurate?

The International 1/4 inch rule, according to the University of Tennessee Extension guide. It allows for taper and kerf losses. Doyle under-scales small logs badly.

Why is Doyle so low for small logs?

Its slab and edging allowance takes 4 in off the diameter whatever the log size. For a 10 in log that removes 40% of the diameter; for a 30 in log, 13%.

How do I measure a log for board feet?

Measure the diameter inside the bark at the small end, to the nearest inch, and the length in feet, then apply the rule your buyer uses.

Sources

Brian Bond, Understanding Log Scales and Log Rules (University of Tennessee Extension PB 1650): Doyle (D – 4) squared x L / 16, Scribner estimate (0.79D squared – 2D – 4) x L / 16, International 1/4 inch equations for 4 to 20 ft logs, Table 3 comparison, price conversion factors

Last reviewed: 25 October 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.