How To Calculate Board Feet In A Log

Estimate lumber yield from a single log or a small load using standard log rules. Enter diameter, length, bark deduction, quantity, and choose Doyle, Scribner, or International 1/4-inch scale to get a practical board foot estimate in seconds.

Tip: Log scaling rules estimate sawn lumber yield, not exact finished boards. For most field use, measure the small-end diameter inside bark whenever possible. If you only have outside-bark diameter, use a bark deduction percentage.

Expert Guide: How to Calculate Board Feet in a Log

Knowing how to calculate board feet in a log is one of the most practical skills in forestry, sawmilling, timber buying, and even hobby woodworking. A board foot is a unit of volume equal to a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long. In simple terms, one board foot equals 144 cubic inches of lumber. However, when you are estimating the yield from a round log, you do not usually calculate raw cubic volume and convert it directly. Instead, most people use a log scale rule, which estimates how many board feet of lumber a log can produce after accounting for slabs, saw kerf, taper, and other milling losses.

That is why a log does not have one universal board foot number. The answer depends on the scaling rule you choose, the log diameter, the length, and whether the diameter is measured inside or outside bark. The three most common rules in North America are Doyle, Scribner, and International 1/4-inch. Each one was created in a different era and each one treats saw kerf and log taper differently, so the estimated yield can vary significantly.

In practical field use, the most important measurements are the small-end diameter and the merchantable log length. If the log is already bucked, you typically scale the small end because it is the limiting size for sawing usable boards. Some buyers and mills specify whether the diameter should be measured inside bark or outside bark with a bark deduction. Always confirm the rule and measuring convention before buying, selling, or tallying logs.

What a board foot means in everyday sawmill terms

A board foot is not the same as a finished board sold at a home center. It is a rough volume measure used in timber and lumber transactions. For example:

• A board that is 1 inch x 12 inches x 12 inches = 1 board foot
• A board that is 2 inches x 6 inches x 8 feet = 8 board feet
• A board that is 1 inch x 8 inches x 10 feet = 6.67 board feet

When you scale logs, you are estimating how many of those board-foot units can reasonably be sawn from the round stem. This is why a scaling rule matters more than a simple cylinder-volume formula.

The core measurements you need

1. Small-end diameter: Measured in inches, usually inside bark for the most accurate log scale estimate.
2. Log length: Measured in feet. Some mills use even lengths such as 8, 10, 12, 14, or 16 feet.
3. Bark deduction: If your diameter is outside bark, subtract a reasonable bark allowance or percentage.
4. Log rule: Doyle, Scribner, or International 1/4-inch.
5. Quantity: Multiply by the number of similar logs if scaling a pile.

The same log can return materially different board-foot estimates depending on the rule used. That is normal. Always compare logs using the same scaling system.

Step-by-step: how to calculate board feet in a log

The fastest workflow is straightforward:

1. Measure the diameter at the small end of the log.
2. Measure the merchantable length in feet.
3. If needed, reduce the diameter for bark.
4. Choose your scaling rule.
5. Apply the rule formula or use a scale table.
6. Multiply by the number of logs.

For calculator purposes, the formulas used are common approximations of standard rules:

• Doyle: ((D – 4)² x L) / 16
• Scribner: ((0.79 x D²) – (2 x D) – 4) x L / 16
• International 1/4-inch: ((0.905 x D²) – (1.221 x D) – 0.719) x L / 16

In these formulas, D is the small-end diameter in inches after bark deduction, and L is log length in feet. These estimates are most useful for conventional sawlog sizes. Very small, very short, crooked, or defective logs may produce less lumber than the rules suggest.

Example calculation

Suppose you have a 16-foot log with a 20-inch small-end diameter inside bark.

• Doyle: ((20 – 4)² x 16) / 16 = 256 board feet
• Scribner: ((0.79 x 400) – 40 – 4) x 16 / 16 = 272 board feet
• International 1/4-inch: ((0.905 x 400) – 24.42 – 0.719) x 16 / 16 = about 337 board feet

You can see immediately why two mills using different scales may quote different values for the same log. Doyle often reads lower on smaller and mid-sized logs, while International tends to be more generous and is often considered more technically refined for a wider range of diameters.

Comparing the Main Log Scale Rules

Each log scale rule reflects assumptions about saw kerf and milling practice from the period in which it was developed. None is universally “right” in every context. The best rule is the one accepted by your local market, your state, your buyer, or your mill.

Doyle rule

Doyle is widely used in parts of the eastern and southern United States. It is easy to calculate and still common in timber trade. The drawback is that it tends to underestimate smaller logs because of the heavy deduction built into the formula. On larger logs, the difference between Doyle and the other rules narrows.

Scribner rule

Scribner is another traditional rule and is commonly seen in log scales and regional timber markets. It was originally based on diagramming boards within a log cross-section. It often produces values between Doyle and International, although the exact relationship depends on log diameter and length.

International 1/4-inch rule

International 1/4-inch is often considered one of the more realistic historical rules because it explicitly tries to account for taper and a quarter-inch kerf. It is frequently favored in technical forestry references when consistent comparisons across log sizes are needed. It usually gives higher values than Doyle for the same log, especially in smaller diameters.

16-foot log diameter	Doyle estimate	Scribner estimate	International 1/4-inch estimate
12 in	64 bf	86 bf	115 bf
16 in	144 bf	166 bf	212 bf
20 in	256 bf	272 bf	337 bf
24 in	400 bf	403 bf	491 bf
28 in	576 bf	559 bf	674 bf

The table shows a real and important pattern: the spread between rules can be substantial. At 12 inches, the difference between Doyle and International is dramatic. At 24 inches and above, the values become closer, but still not identical. That is why timber appraisals and private sales should always specify the log rule in writing.

How length changes the estimate

Length matters because a longer log contains more recoverable lumber. If diameter stays fixed, the board-foot estimate scales roughly in proportion to length. Below is a comparison for a 20-inch log.

20-inch log length	Doyle	Scribner	International 1/4-inch
8 ft	128 bf	136 bf	168 bf
10 ft	160 bf	170 bf	211 bf
12 ft	192 bf	204 bf	253 bf
16 ft	256 bf	272 bf	337 bf
18 ft	288 bf	306 bf	379 bf

These comparisons are useful for planning sawmill yield, estimating stumpage value, and deciding how to buck a stem. In some situations, adding a little extra merchantable length can materially increase scale volume, provided sweep and defect stay acceptable.

Common Mistakes When Estimating Board Feet

1. Measuring outside bark without adjusting

Bark adds diameter but does not become lumber. If you use outside-bark diameter without a deduction, you will overstate yield. Thick-barked species can be especially misleading.

2. Measuring the wrong end of the log

Standard scaling usually relies on the small-end diameter because it represents the limiting cross-section for sawing. Measuring the butt end instead can inflate the estimate significantly.

3. Ignoring defects

Rot, crook, sweep, checks, shake, and excessive taper all reduce the amount of recoverable lumber. A scale rule gives a baseline estimate for a reasonably sound log. It does not replace a grader or scaler’s judgment.

4. Mixing scaling rules in one comparison

If one buyer quotes Doyle and another quotes International, the numbers are not directly comparable. Convert them mentally only with caution. The cleaner approach is to ask both buyers to quote under the same rule or compare on price per ton, cubic volume, or delivered mill scale, depending on your market.

5. Forgetting trim allowances

Logs are often bucked with trim in mind. If your sale specification requires exact nominal lengths plus trim, make sure that the actual merchantable length reflects the mill’s requirements.

6. Treating board feet as identical to finished output

Board-foot scale is an estimate of rough lumber potential. Finished, surfaced, dried, or defect-free boards from the same log will usually total less than the initial gross scale.

When to use cubic feet instead

Board feet are ideal for sawlogs and lumber-oriented markets, but cubic volume is often more neutral for research, biomass work, and mixed-product forestry. Cubic volume measures the wood content itself, while board-foot scale estimates lumber yield. Both can be useful at the same time. That is why the calculator above also reports an estimated cubic-foot volume based on adjusted diameter and length.

Practical field tips for better accuracy

• Use a log rule stick or diameter tape if you scale frequently.
• Measure on the small end where the cut is square and clear.
• Record whether the measurement is inside bark or outside bark.
• Separate logs by species and quality if they will be sold differently.
• Keep notes on defect deductions so your tally can be audited later.
• Confirm with the buyer which rule controls payment.

Authoritative references

For deeper technical reading, review guidance from authoritative forestry sources such as the Penn State Extension guide to tree and log scaling, the University of Kentucky Forestry log scale reference, and the U.S. Forest Service for broader mensuration and forest measurement resources.

Bottom line

If you want to know how to calculate board feet in a log, start with the small-end diameter, log length, and the correct log rule. Use Doyle, Scribner, or International 1/4-inch consistently, apply a bark deduction when needed, and remember that the result is an estimate of lumber yield rather than a promise of exact finished boards. For buying, selling, or planning a milling project, consistency matters even more than the specific rule chosen. The calculator on this page gives you a fast estimate and a side-by-side chart so you can understand how the major rules differ before you make a decision.