How Many Board Feet Are in a Log?

The Doyle rule

The Doyle rule is the most used log scale in the eastern United States for estimating how many board feet of lumber a log will yield. The formula:

Board feet = (D - 4)^2 x L / 16

where D is the small-end diameter inside the bark, in inches, and L is the log length in feet. Measure the diameter at the small end because the sawyer can only cut boards as wide as the narrow end allows.

Worked example 1: 20-inch diameter, 16 feet long

(20 - 4)^2 x 16 / 16 = 16^2 = 256 board feet. That is a solid sawlog, roughly enough 4/4 lumber to build a large dining table with waste to spare.

Worked example 2: 12-inch diameter, 10 feet long

(12 - 4)^2 x 10 / 16 = 64 x 10 / 16 = 40 board feet. Small logs scale harshly under Doyle, which is the rule's famous bias. A 12-inch log really does yield little usable lumber once you account for slab loss, taper, and the saw kerf, but Doyle is widely considered to undercount small logs relative to what a modern mill recovers.

Worked example 3: 24-inch diameter, 12 feet long

(24 - 4)^2 x 12 / 16 = 400 x 12 / 16 = 300 board feet. Big, straight logs are where Doyle shines and where the money is: one 24-inch butt log can hold more board feet than a whole pile of small ones.

Why Doyle subtracts 4

The minus 4 is a fudge factor for everything the sawmill loses: the rounded slab cut off each side, the saw kerf (about 1/4 inch per cut on a circle mill, less on a bandsaw mill), taper along the log, and edging waste. Squaring the remainder approximates the cant, the squared-up block of wood the mill actually saws into boards. Dividing by 16 converts the cubic-inch-ish result into board feet for the given length.

Doyle vs Scribner vs International 1/4-inch

Three log rules dominate American timber, and they disagree, so know which one your buyer uses before you negotiate:

• Doyle: the formula above. Underestimates small logs, widely used in the eastern US for hardwood.
• Scribner: based on diagrams of how many 1-inch boards fit in circles of each diameter. A 20-inch, 16-foot log scales about 280 board feet under Scribner, a bit more generous than Doyle's 256. Common in the western US and for softwood.
• International 1/4-inch: the most mathematically careful, accounting for 1/4-inch kerf, taper, and standard board sizes. It typically estimates the highest of the three, especially on small logs. Used officially by the US Forest Service and considered the fairest.

The practical takeaway: a log's scaled board feet are a negotiating unit, not a physical constant. A log that scales 256 Doyle might scale 300 International. When selling timber, ask which rule the buyer scales on, because the rule choice moves the price.

How to measure a log for scaling

1. Diameter: measure inside the bark at the small end, in inches. If the end is oval, average the long and short axes. Round down to the nearest inch; that is standard.
2. Length: measure in feet, including the standard trim allowance (usually 4 to 6 inches over the nominal length, which the mill needs for end trimming).
3. Deductions: scale rules assume a sound, straight log. Sweep (curve), rot, and large knots get deducted by the scaler, sometimes substantially. A hollow butt log can lose half its scale or be rejected outright.

From log scale to lumber in your shop

Log scale estimates what the mill recovers, not what you take home. Drying, planing, and your own milling waste shrink it further. As a rough planning number, expect 10 to 20 percent loss from scaled board feet to usable surfaced lumber, more if the logs are small or defective. And when those boards are milled, they get priced and counted with the standard board foot formula, nominal dimensions, divided by 12.

Common mistakes

Measuring the big end. Scale on the small-end diameter. The big end flatters the log and every buyer will re-measure it your way.

Measuring outside the bark. Bark is not lumber. Measure inside the bark, or deduct roughly an inch for thick bark on species like oak.

Treating scale as a guarantee. Doyle on small logs notoriously underestimates what a thin-kerf bandsaw mill recovers, which is good news for the buyer of the lumber and bad news for the seller of the log. Know the bias of the rule in play.

Forgetting trim. Logs are cut long for a reason. If you buck firewood-length logs and call them sawlogs, the mill cannot use them, and no scale rule fixes that.