About the Log Board Feet Calculator
This log board feet calculator estimates how much sawn lumber a log will yield, using the three log rules most often used in North American timber sales: Doyle, Scribner and International ¼-inch. Enter the diameter inside the bark at the small end of the log and its length in feet, and the tool scales the log under each rule side by side, multiplies by the number of logs and estimates the value at your price per thousand board feet (MBF).
It is useful for woodlot owners weighing a timber offer, people buying sawlogs for a portable sawmill and anyone curious why buyers and sellers quote different volumes for the same logs. The rules disagree most on small logs: Doyle heavily under-scales logs under about 20 inches, Scribner sits in the middle, and International ¼" is the closest to what an efficient mill actually saws.
Measure the small-end diameter inside the bark to the nearest inch (average two measurements at right angles if the end is oval) and the length in feet, ignoring the few inches of trim allowance. Log rules ignore defects such as rot, sweep and crook, so real yield from a given log may be lower.
With the default inputs, the board feet (selected rule) is 181 bd ft. Change any value above to recalculate instantly.
How to use the log board feet calculator
- 1Measure the diameter inside the bark at the small end of the log, in inches.
- 2Measure the log length in feet, excluding trim allowance.
- 3Enter how many logs of this size you have.
- 4Choose the log rule used in your sale and enter the price per thousand board feet.
- 5Compare the three rules and the scale table before agreeing a price.
Formula and method
All three rules use the small-end diameter inside bark (D, inches) and the log length (L, feet). The Doyle rule deducts 4 inches from the diameter for slabs and edgings, which makes it severely under-scale small logs. The Scribner rule was originally a set of diagrams of 1-inch boards drawn inside circles; the formula shown is the standard algebraic approximation of those values.
The International ¼-inch rule treats the log as 4-foot sections, assuming the diameter grows by ½ inch every 4 feet toward the butt. Each section yields 0.22d² − 0.71d board feet for a ⅛-inch saw kerf, and the total is multiplied by 0.905 to allow for a ¼-inch kerf. Lengths that are not a multiple of 4 feet get a proportional share of the next section. Value is board feet ÷ 1,000 × price per MBF.
- D
- Small-end diameter inside bark, inches
- L
- Log length, feet
- d
- Diameter at the small end of each 4-ft section, inches
Worked examples
16-inch × 16-foot sawlog
Doyle gives (16 − 4)² × 16 ÷ 16 = 144 bd ft, Scribner (0.79 × 256 − 32 − 4) = 166 bd ft, and International ¼" sums four 4-ft sections (44.96 + 48.18 + 51.51 + 54.95 = 199.6) × 0.905 ≈ 181 bd ft. At $350 per MBF that log is worth about $63.
Five 12-inch × 12-foot logs sold on Doyle
Each log scales 48 bd ft by Doyle but about 69 bd ft by International ¼", so five logs total 240 versus 347 bd ft. Selling small logs on Doyle at $350 per MBF pays only $84 for wood that would saw out much more.
Three 24-inch × 10-foot logs on Scribner at $400/MBF
Large logs bring the rules close together: three 24-inch, 10-foot logs scale 750 bd ft by Doyle, 756 by Scribner and 772 by International ¼". On Scribner at $400 per MBF they are worth about $302.
Frequently asked questions
What is a board foot?+
A board foot is a volume of wood 12 inches long, 12 inches wide and 1 inch thick, or 144 cubic inches. Log rules estimate how many board feet of lumber a log will produce after slabs, edgings and saw kerf are removed.
Which log rule is most accurate?+
The International ¼-inch rule is generally considered the closest to actual mill output across all log sizes. Doyle badly under-estimates small logs and over-estimates very large ones, while Scribner is reasonable for medium and large logs.
Why does Doyle give lower numbers for small logs?+
The Doyle formula subtracts 4 inches from the diameter before squaring it, an allowance that is far too large for small logs. A 12-inch log loses a third of its diameter, so Doyle scales it well below what it actually saws.
Where do I measure log diameter?+
Measure inside the bark at the small end of the log. If the end is not round, take the shortest and longest diameters through the center and average them, rounding down to the nearest whole inch as scalers usually do.
What is MBF in timber prices?+
MBF means one thousand board feet. A price of $350/MBF means each board foot is worth $0.35, so a log scaling 200 board feet is worth $70 at that price under the agreed log rule.