Calculating Board Feet Of A Log

Forestry Calculator

Estimate log volume in board feet using three common log rules: Doyle, Scribner, and International 1/4-inch. Enter the small-end diameter, merchantable log length, and number of logs to get an instant estimate and a side-by-side chart.

• Board feet represent lumber volume equivalent to a board 1 inch thick, 12 inches wide, and 12 inches long.
• These log rules are estimates, not guaranteed sawmill yield.
• Actual recovery varies with taper, defects, sweep, rot, trim allowance, and mill technology.

Expert Guide to Calculating Board Feet of a Log

Calculating board feet of a log is one of the most important skills in forestry, sawmilling, timber purchasing, and woodland management. Whether you are a landowner preparing to sell timber, a sawyer estimating yield, or a woodworker trying to understand how much lumber a log may contain, board-foot scaling gives you a common language for volume. A board foot is the volume of a piece of wood that measures 1 inch thick, 12 inches wide, and 12 inches long. When applied to logs, however, the calculation is not as simple as converting a cylinder into cubic volume. Logs are usually scaled using standard log rules that estimate the amount of lumber that can be sawn from a round log after accounting for slabs, saw kerf, taper, and waste.

The reason this matters is straightforward: two logs with the same diameter and length can be valued differently depending on the log rule used. In North America, the three most common scale rules are Doyle, Scribner, and International 1/4-inch. Each rule was designed to estimate lumber recovery, but they do so differently. That means understanding your rule is just as important as measuring the log correctly. If you use the wrong rule, you may overestimate or underestimate value, especially on small or medium diameter logs.

The most practical workflow is this: measure the small-end diameter inside bark, measure the merchantable length, select the log rule required by your buyer or region, and then calculate board-foot scale. This calculator automates that process and also compares all three rules side by side.

What board feet means in practical terms

Board feet are a lumber measure, not a direct measure of geometric log volume. If you calculate the cubic volume of a log, you are measuring the total wood space inside the bark. A board-foot rule goes a step further and estimates how much sawn lumber could be recovered. That is why board-foot scaling is more useful than simple cubic footage when buying or selling sawtimber.

For example, a straight, sound 16-foot log with a 16-inch small-end diameter may scale very differently under each rule. The Doyle rule typically gives a lower estimate for smaller logs because it assumes relatively large losses to slabs and saw kerf. The International 1/4-inch rule was designed to better reflect actual lumber recovery, especially across a broader range of diameters. Scribner generally falls somewhere between the two.

The measurements you need before calculating

Before you can estimate board feet of a log accurately, you need sound field measurements. The quality of your scaling estimate depends on good measurement practice.

• Small-end diameter inside bark: This is the most commonly used diameter for scaling. Measure across the small end of the log, excluding bark if possible.
• Merchantable length: This is the usable section of the log that can be milled. Trim allowance and defects can reduce this figure.
• Log rule: Confirm whether the local mill or buyer uses Doyle, Scribner, or International 1/4-inch.
• Log condition: Sweep, crook, rot, cracks, burn, and insect damage can all reduce actual yield and may require deductions.
• Number of logs: If you are scaling a load, tract, or deck, multiply per-log scale by total count when logs are uniform, or scale individually when they are not.

Common formulas used to estimate board feet

There are many scale tables in forestry references, but modern calculators often use formula approximations. The calculator above uses these standard approximations with diameter in inches and length in feet:

1. Doyle: ((D – 4)² × L) ÷ 16, for logs larger than 4 inches in diameter.
2. Scribner: ((0.79 × D²) – (2 × D) – 4) × L ÷ 16.
3. International 1/4-inch: ((0.905 × D²) – (1.221 × D) – 0.719) × L ÷ 16.

These formulas are widely used for quick estimation, but in professional timber transactions, official regional scale tables, grading rules, and scaler deductions may also apply. The point is not just to get a number. The point is to get the right number under the rule your market recognizes.

How the three main log rules differ

The Doyle rule is common in many hardwood-producing regions of the United States. It is simple and widely recognized, but it tends to underestimate smaller logs. Because of this, buyers and sellers who use Doyle should be especially careful when discussing value on logs under about 20 inches in diameter.

The Scribner rule is based on diagrams of boards that could be sawn from a log. It often produces values higher than Doyle on small and medium logs, but lower than International 1/4-inch. It remains common in parts of the western United States and in some timber markets where it has historical use.

The International 1/4-inch rule was designed to better represent actual mill output by accounting for taper and a 1/4-inch saw kerf. Many foresters consider it one of the more consistent rules across a range of diameters and lengths. If your objective is to estimate likely lumber recovery rather than follow a traditional local buying rule, International 1/4-inch is often the most informative comparison benchmark.

Small-end diameter	16-foot Doyle	16-foot Scribner	16-foot International 1/4-inch
10 inches	36 bd ft	55 bd ft	78 bd ft
12 inches	64 bd ft	86 bd ft	115 bd ft
14 inches	100 bd ft	123 bd ft	160 bd ft
16 inches	144 bd ft	166 bd ft	211 bd ft
18 inches	196 bd ft	216 bd ft	271 bd ft
20 inches	256 bd ft	272 bd ft	337 bd ft

This table illustrates the biggest lesson in log scaling: the rule matters. On a 16-foot, 16-inch log, Doyle yields 144 board feet, Scribner yields 166 board feet, and International 1/4-inch yields 211 board feet. That spread is large enough to influence pricing, harvest planning, and contract expectations. If one party is mentally estimating under one rule while the transaction is written under another, confusion is almost guaranteed.

Step-by-step method for measuring a log in the field

1. Identify the merchantable stem and determine where the usable log begins and ends.
2. Measure the small-end diameter at the narrow end of the log segment. If bark must be included in the field measurement, use a local bark deduction standard if available.
3. Measure merchantable length in feet, or in meters if your tool requires conversion.
4. Choose the correct scaling rule for your region or intended market.
5. Apply the formula or scale table to estimate board-foot volume.
6. If there are multiple logs from the same tree, scale each separately because diameter and taper change from butt log to upper logs.
7. Apply deductions for major defects when doing a professional timber estimate.

Why actual lumber yield can differ from board-foot scale

Even the best scaling rule is still an estimate. Actual lumber recovery depends on many variables that a simple log formula cannot fully capture. Species matters because some species have thicker bark, more frequent defect patterns, or more sweep. Log form matters because straight logs produce better recovery than crooked ones. Sawing method matters because band saws, circular saws, and optimized scanning systems all recover different amounts of lumber. Moisture content, trim requirements, and grade cuttings also influence final yield.

A modern mill may recover more lumber from a given log than older scale rules assume. That is one reason why historic rules can diverge from actual sawmill production. Still, those same rules remain commercially important because they are deeply embedded in timber pricing conventions.

Log size example	Doyle estimate	Scribner estimate	International 1/4-inch estimate	Difference between highest and lowest
12 in × 16 ft	64 bd ft	86 bd ft	115 bd ft	51 bd ft
16 in × 16 ft	144 bd ft	166 bd ft	211 bd ft	67 bd ft
20 in × 16 ft	256 bd ft	272 bd ft	337 bd ft	81 bd ft

Notice how the spread between rules remains economically meaningful as log diameter increases. This is why timber contracts should always specify both the unit of sale and the scale rule. Saying a load contains a certain number of board feet is incomplete unless the rule is clear.

Useful tips for landowners and buyers

• Always ask which log rule the mill uses before comparing price quotes.
• Measure several logs to spot-check buyer estimates, especially if you are new to timber sales.
• When comparing bids, convert all offers to the same unit and same rule if possible.
• Remember that board-foot value and grade value are different. A lower-volume, higher-grade log may be worth more than a larger but defective one.
• Use board-foot scaling for sawlogs, but use other units such as cords, tons, or cubic measures where those are standard for pulpwood or biomass.

Recommended authoritative references

If you want deeper technical guidance, these sources are excellent starting points:

• U.S. Forest Service for timber measurement, scaling references, and forest management publications.
• University of Minnesota Extension for woodland measurement, timber sale preparation, and practical forestry education.
• Penn State Extension for woodland owner guidance on log scaling, timber marketing, and forest economics.

Final takeaways on calculating board feet of a log

To calculate board feet of a log correctly, you need more than diameter and length. You also need the right scaling rule. The most reliable field process is to measure the small-end diameter inside bark, measure merchantable length carefully, and apply the specific log rule used by your buyer or region. Doyle is common but often conservative on small logs. Scribner is widely recognized and often intermediate. International 1/4-inch is frequently closer to theoretical lumber recovery across varied log sizes.

For practical decision making, use the calculator above to estimate all three rules every time. That gives you a stronger negotiation position, helps you understand market differences, and makes your timber inventory more credible. If the estimate will affect a significant timber sale, it is wise to consult a professional forester, extension specialist, or certified timber buyer. A precise scale, especially when paired with log grades and defect deductions, can have a major effect on total sale value.

Educational note: calculator outputs are planning estimates intended for informational use. Official timber transactions may use local scale tables, trim allowances, and defect deductions that differ from this simplified model.