Doyle vs Scribner vs International Log Rules

What Is a Log Rule?

A log rule is a table or formula that estimates how many board feet of lumber can be sawn from a given log. Unlike the simple board foot formula (T × W × L ÷ 12), log rules try to account for the reality of milling: the saw blade removes material (kerf), the log is not perfectly square, and the outer slabs are waste. Different rules make different assumptions about these factors, which is why the same log can produce different estimates depending on which rule you use.

The Doyle Rule

The Doyle Rule is the oldest and most widely used log rule in the eastern United States, especially for hardwood. The formula is:

Diameter is measured in inches at the small end of the log, inside the bark. Length is in feet.

The Doyle Rule subtracts 4 inches from the diameter to account for saw kerf and slab waste before squaring. This means it underestimates volume for small logs (under 28 inches) and overestimates for large logs. If you are selling small-diameter hardwood logs, you will get a lower board foot estimate under Doyle than under other rules — which matters when you are negotiating a price.

For example, a 16-inch diameter log that is 12 feet long gives:

The Scribner Decimal C Rule

The Scribner Rule is based on diagrams of log cross-sections showing how many boards of standard thickness could be cut. The Decimal C version rounds the result to the nearest 10 board feet, making it easier to use in the field. It does not have a simple formula — it uses a table of values derived from those diagrams.

For the same 16-inch, 12-foot log, Scribner typically estimates around 130-140 board feet, which is higher than Doyle. Scribner is commonly used in the western US for softwood timber sales. It tends to be more accurate than Doyle for medium-sized logs because it is based on actual mill yields rather than a simplified formula.

One drawback of Scribner is that it does not account for log taper, so longer logs can be slightly underestimated.

The International 1/4-Inch Rule

The International Rule, developed at the University of Michigan, is considered the most accurate of the three. It accounts for log taper and uses a 1/4-inch kerf (saw blade thickness). It is more complex mathematically, involving a formula that adjusts for each additional foot of length.

For the same 16-inch, 12-foot log, the International Rule estimates around 145-155 board feet. It is most commonly used by professional foresters and for timber appraisals where accuracy matters more than convenience.

The International Rule is also the most generous — it gives the highest board foot estimate of the three for most log sizes because it assumes the most efficient milling.

Comparison Table

Which Rule Should You Use?

It depends on where you are and what you are selling. In the eastern US hardwood market, Doyle is the standard. Most sawmills and timber buyers will quote you in Doyle. In the western US softwood market, Scribner is more common. The International Rule is typically used for timber cruises and appraisals where precision is the priority.

If you are buying logs, knowing the rule matters because the same log can vary by 20-30% between Doyle and International. A seller quoting Doyle will give you a lower number than the same seller quoting International, even though the log is identical. Always ask which rule is being used.

If you are measuring lumber that has already been milled into boards (not logs), these rules do not apply. Use the standard board foot formula instead.