Woodworking calculator
Log Board Foot Calculator (Doyle Rule)
Before a log reaches the sawmill, buyers and sellers need to estimate how many board feet of lumber it will produce. This calculator uses the Doyle log rule to turn a log small-end diameter and length into an estimated board foot yield, and explains how Doyle compares to the International and Scribner scales. Because the rules disagree, especially on small logs, understanding the spread helps you avoid overpaying or undervaluing timber when buying or selling.
This tool uses the Doyle rule, a clean formula that matches published Doyle scale tables exactly. The International 1/4-inch and Scribner rules are table-based and vary by source; for an official scale use a printed International or Scribner table or a forester.
How it works
A log rule is a formula or table that estimates the lumber yield of a log from its small-end diameter inside the bark and its length. Several rules exist because they were developed in different regions and eras with different assumptions about saw kerf, taper, and slab waste, so they give different numbers for the same log.
The Doyle rule subtracts four inches from the diameter for slab and edging allowance, squares a quarter of the remainder, and multiplies by length. It is simple and widely used in the eastern and southern United States, but it badly underestimates small logs and overestimates very large ones. The Scribner rule is a diagram based rule that counts boards drawn inside the log circle and reads between Doyle and International. The International quarter inch rule sums the yield of short sections and includes a realistic taper and kerf allowance, which makes it the most accurate and the closest to actual mill output across log sizes.
Inputs are the small-end diameter in inches, measured inside the bark, and the log length in feet. Because the rules diverge, the same log can scale very differently: Doyle may show far fewer board feet than International on a small log, which matters a great deal when money changes hands. This tool computes the Doyle rule, which matches published Doyle scale tables exactly; for the International and Scribner scales, which vary by source, use a printed scale table or a forester.
Worked example
A 20 in small-end x 16 ft log by Doyle: ((20 - 4) / 4)² x 16 = 256 board feet. This matches the published Doyle log-rule table for that size.
Frequently asked questions
What is a log rule?
A log rule is a formula or table that estimates the board feet of lumber a log will yield from its small-end diameter and length. Different rules make different allowances for saw kerf, taper, and slab waste, so they disagree.
Why do Doyle and International give different numbers?
They were built on different assumptions. Doyle uses a fixed four inch slab deduction that overstates waste on small logs, while the International rule models taper and a thin kerf section by section, so it tracks actual mill output more closely.
Which log rule is most accurate?
The International quarter inch rule is generally considered the most accurate because it accounts for taper and realistic kerf. Doyle is simpler and common in the South and East but underestimates small logs and overestimates large ones.
How do I measure the log diameter?
Measure the diameter at the small end of the log, inside the bark, in inches. If the end is oval, average the shortest and longest measurements. Small-end diameter is used because it sets the limiting size of boards the log can produce.
Are these estimates exact yields?
No, they are estimates. Actual board foot recovery depends on log quality, defects, taper, the saw kerf, and the sawyer skill. Treat the numbers as a fair basis for pricing and comparison rather than a guaranteed output.
Related calculators
Sources
These calculators are for planning and estimation. Engineering results (shelf sag, wood movement) use published average material properties; real boards vary by grade, grain, moisture and defects. Verify load-bearing designs with a professional.