Log Scale Calculator (Doyle, Scribner, International)
Estimate the board feet you can saw from a log with the three standard log rules, side by side.
Common in the eastern US; underscales small logs.
Diagram rule, widely used by the US Forest Service.
Most accurate; the reference standard for saw yield.
Diameter is measured inside the bark at the small end of the log. The three rules disagree on purpose: Doyle undercounts small logs, the International 1/4" rule is the most accurate estimate of actual sawn yield, and Scribner sits in between. Ask your mill which rule they buy and sell by before you price a log.
How log rules work
A log rule estimates how many board feet of lumber a log will yield. You measure the small-end diameter inside the bark in inches and the length in feet, and the rule returns board feet. There is no single correct answer, because the rules make different assumptions about saw kerf, taper, and slab loss.
The three rules
Doyle is the most common rule in the eastern United States. It is easy to compute but it undercounts small logs badly, which favors the buyer. A 12 inch log looks a lot smaller under Doyle than it really is.
Scribner (the Decimal C version rounds to the nearest 10 board feet) is a diagram rule from the 1800s that is still used widely, including by parts of the US Forest Service. It sits between Doyle and International for mid-size logs.
International 1/4 inch is the most accurate estimate of what a modern thin-kerf saw actually produces. Foresters treat it as the reference standard. If you want to know true yield, use this one.
Which rule to use
Use the rule your mill buys and sells by, because that is the number that sets the price. If you are estimating your own yield for milling, the International 1/4 inch figure is closest to reality. The gap between rules is largest on small logs, so on a load of small-diameter timber the choice of rule can change the value by a lot.
Frequently asked questions
- Why do the three log rules give different answers?
- They make different assumptions about saw kerf, taper, and slab waste. Doyle assumes a wide kerf and undercounts small logs, International 1/4 inch models a thin kerf and real taper, and Scribner falls in between.
- Which log rule is most accurate?
- The International 1/4 inch rule. It is the standard foresters use to estimate real sawn yield and it tracks modern thin-kerf sawing closely.
- How do I measure log diameter?
- Measure across the small end of the log, inside the bark, in inches. If the end is oval, average the smallest and largest measurements.
- What length should I enter?
- The log length in feet. Most log rules are built around even foot lengths, so round to the nearest even foot.