Calculate Board Feet of Log
Estimate log volume in board feet using the Doyle, Scribner, or International 1/4-inch log rule. Enter the small-end diameter inside bark, log length, and quantity to get a fast, practical estimate for milling, timber buying, and forestry planning.
Log Volume Calculator
Expert Guide: How to Calculate Board Feet of a Log Accurately
Learning how to calculate board feet of a log is one of the most useful skills in forestry, sawmilling, timber buying, and small woodlot management. Whether you are pricing standing timber, estimating sawmill output, or comparing what different mills might pay, board foot scaling gives you a common language for lumber volume. A board foot is a measure of wood volume equal to 144 cubic inches, which is the same as a board that is 12 inches by 12 inches by 1 inch thick. Logs, however, are round and irregular, so the board foot content of a log is never measured as a simple geometric conversion. Instead, foresters and mills usually rely on log rules that estimate how much sawn lumber a log could produce.
The three best-known log rules in the United States are Doyle, Scribner, and International 1/4-inch. Each rule uses a slightly different assumption about slab loss, saw kerf, and sawing pattern. That means the same exact log can produce three different board foot estimates depending on the rule selected. This is why it is essential to know not just the diameter and length of the log, but also the measurement standard used by the buyer, logger, broker, or mill. If you compare timber offers without matching log rules, you can easily misunderstand the real value of a load or tract.
What measurements you need before you calculate
At minimum, most board foot calculations require two measurements: the small-end diameter inside bark and the merchantable length of the log. The small end is used because it limits the largest square or rectangular cant that can be sawn from the log. Inside-bark diameter is more accurate than outside-bark diameter because bark thickness does not become lumber. Merchantable length is the usable straight section that meets the buyer’s minimum standards. In many markets, logs are cut in even lengths with trim allowance, but exact conventions vary by region.
- Diameter: Usually measured at the small end inside bark, in inches.
- Length: Measured in feet, sometimes with an added trim allowance.
- Quantity: Number of similar logs if you want a grouped estimate.
- Log rule: Doyle, Scribner, or International 1/4-inch depending on the market.
Good measurement technique matters. If the log is out of round, scalers often average the smallest and largest diameters. If the log has sweep, heavy taper, hollow sections, or visible rot, deductions may apply. A simple calculator can estimate gross board feet, but net scale may be lower once defects and quality are considered.
The most common formulas used to estimate board feet
The Doyle rule is often written as ((D – 4)² × L) / 16, where D is diameter in inches and L is length in feet. This rule is simple and widely recognized, but it is known for underestimating small logs because the 4-inch deduction is severe when diameter is low. As diameter increases, Doyle estimates become more favorable.
The Scribner Decimal C rule is commonly approximated as ((0.79 × D²) – (2 × D) – 4) × L / 16. This rule is based on a sawing diagram and generally gives higher values than Doyle for smaller and medium logs. It is often used in western and mixed-species markets, although local practice still matters.
The International 1/4-inch rule is commonly approximated by (0.22 × D² – 0.71 × D) × (L / 4). Many foresters consider this the most technically balanced of the three common rules because it accounts more realistically for saw kerf and taper than older rules. It often produces a value between practical mill recovery expectations and scaling convention, though the actual lumber yield still depends on the equipment, sawing pattern, operator skill, and defect level.
Worked example: 18-inch diameter, 16-foot log
Suppose you have one hardwood log measuring 18 inches at the small end inside bark and 16 feet in length. Using standard approximations:
- Doyle: ((18 – 4) × (18 – 4) × 16) / 16 = 196 board feet
- Scribner: ((0.79 × 18²) – (2 × 18) – 4) × 16 / 16 = about 216 board feet
- International 1/4-inch: (0.22 × 18² – 0.71 × 18) × (16 / 4) = about 234 board feet
That spread is large enough to affect pricing, trucking decisions, and harvest planning. If a buyer quotes a price per thousand board feet under the Doyle rule and another quotes under the International rule, those numbers are not directly comparable. Always ask, “Price per thousand by which scale?” before deciding which offer is better.
Comparison table: same log, different log rules
| Small-end diameter | Length | Doyle BF | Scribner BF | International 1/4-inch BF |
|---|---|---|---|---|
| 12 in | 16 ft | 64 | 86 | 99 |
| 14 in | 16 ft | 100 | 123 | 148 |
| 16 in | 16 ft | 144 | 166 | 202 |
| 18 in | 16 ft | 196 | 216 | 234 |
| 20 in | 16 ft | 256 | 272 | 323 |
This table illustrates an important pattern: the Doyle rule starts comparatively low on smaller logs and narrows the gap as diameter increases. International 1/4-inch usually gives the highest estimate in these examples because it captures sawable potential more generously for many medium-size logs.
Why board foot estimates differ from actual sawmill output
Board foot scale is an estimate of potential lumber yield, not a guarantee. In real mill conditions, actual output can be lower or higher depending on several factors. Species matters because hardwood and softwood logs are sawn differently and can have different taper patterns. Defect matters because rot pockets, shake, knots, crook, and metal damage reduce recovery. Mill technology matters because a modern thin-kerf band mill loses less wood to sawdust than an older circular mill. Operator decisions also matter. A skilled sawyer can often turn a borderline log into a better mix of boards than a novice can.
- Log taper reduces recoverable volume in the upper part of the stem.
- Sweep and crook reduce the amount of straight lumber that can be sawn.
- Rot, splits, and ring shake create waste and downgrade boards.
- Saw kerf and edging methods change how much wood becomes salable lumber.
- Trim loss and target dimensions influence final recovery.
For that reason, some mills settle on gross scale and others on net scale. Gross scale means the volume before defect deductions. Net scale means deductions have been applied for defects, cull, or unusable sections. If you are selling timber, verify whether the ticket or contract is gross or net and ask how deductions are assigned.
Board feet versus cubic feet and why it matters
Board feet and cubic feet are both measures of volume, but they are not interchangeable in practice. One board foot contains one twelfth of a cubic foot of solid wood. If a log contained 120 board feet of solid sawn-lumber equivalent, that would equal 10 cubic feet of wood volume. However, logs are scaled by sawmill yield assumptions, so a 120-board-foot scale estimate is not simply the same thing as the geometric cubic volume of the round log. Forest inventory systems may report timber volume in cubic feet, cords, or board feet depending on product class and region. Understanding the difference prevents confusion when comparing standing volume reports, mill settlements, and transport estimates.
Comparison table: common board foot equivalents for lumber planning
| Nominal board size | Length | Board feet per piece | 10 pieces total |
|---|---|---|---|
| 1 x 6 | 8 ft | 4 BF | 40 BF |
| 2 x 4 | 8 ft | 5.33 BF | 53.3 BF |
| 2 x 6 | 10 ft | 10 BF | 100 BF |
| 2 x 8 | 12 ft | 16 BF | 160 BF |
| 4 x 4 | 10 ft | 13.33 BF | 133.3 BF |
This second table is useful because it connects log scaling with project planning. If your log estimate is 200 board feet, you can quickly judge whether the log is likely to cover a framing package, barn repair, furniture stock, or custom sawn boards. Keep in mind that rough-sawn output, edging waste, and drying shrinkage all affect the final tally.
Best practices for landowners, sawyers, and timber buyers
If you own woodland and plan to sell logs, use one consistent measurement method from the start. Record species, diameter, merchantable length, and visible defects. Photograph representative logs and ask buyers to specify the scaling rule in writing. If possible, compare mill settlement sheets to your own field estimates after each sale. This feedback loop helps you calibrate future estimates and understand whether your local market tends to favor one rule over another.
- Measure the small-end diameter inside bark.
- Measure merchantable length in feet.
- Select the correct local log rule.
- Calculate gross board feet.
- Apply deductions for defect if needed.
- Compare with mill scale tickets and adjust your process over time.
Portable sawmill operators can also benefit from board foot estimation because it helps with quoting. If you charge by the board foot, explain whether pricing is based on log scale, sawn tally, or final dry tally. Those are different billing bases. A customer may assume one thing while the operator means another, so clarity avoids disputes.
Authoritative resources for timber measurement
For deeper reference material on scaling, forest inventory, and timber measurement, review these trusted sources:
Final takeaway
To calculate board feet of a log, you need more than just a tape measure. You need the correct diameter point, the correct merchantable length, and the correct scaling rule for your market. Doyle, Scribner, and International 1/4-inch can all produce useful estimates, but they should never be treated as interchangeable. For routine decision-making, use a calculator like the one above, save your inputs, and compare estimates across rules before negotiating prices or scheduling milling. The more disciplined your measurement process is, the more confident you can be in your timber valuation, lumber planning, and harvest decisions.