How Do You Calculate Board Feet In A Log

Use this interactive log scale calculator to estimate board feet from log diameter and length. Compare cylindrical volume, Doyle, Scribner, and International 1/4-inch estimates, then review the expert guide below to understand which method fits your mill, timber sale, or firewood to sawlog evaluation.

Expert Guide: How Do You Calculate Board Feet in a Log?

If you have ever asked, “how do you calculate board feet in a log,” you are asking one of the most important questions in forestry, sawmilling, timber buying, and custom woodworking. A board foot is a unit of volume used for lumber, and it equals a piece of wood that is 12 inches long, 12 inches wide, and 1 inch thick. That means one board foot equals 144 cubic inches, or 1/12 of a cubic foot. Logs, however, are round, tapered, and imperfect, so converting a standing tree or a cut log into board feet requires either a geometric estimate or a standard log rule.

In practice, professionals rarely rely on a single universal formula for every situation. Instead, they choose a method based on the purpose of the estimate. If you want a simple physical volume estimate, you can calculate the cylindrical volume of the log and convert that to board feet. If you are buying or selling sawlogs, you are more likely to use a recognized log rule such as the Doyle rule, Scribner rule, or International 1/4-inch rule. These scaling rules were developed to estimate the amount of sawn lumber a log might produce after accounting for slabs, saw kerf, and waste.

What is a board foot?

A board foot is not the same as a cubic foot, even though both measure volume. In lumber terms, one board foot is:

• 12 inches × 12 inches × 1 inch
• 144 cubic inches
• 0.0833 cubic feet

This matters because lumber thickness is usually expressed in inches while log length is often measured in feet and diameter is measured in inches. A good board foot calculation converts these dimensions consistently. If you are measuring a sawn board, the basic formula is straightforward:

Board feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12

Logs are harder because they are round, so you need to estimate how much lumber can be cut from that round shape.

The simplest way: estimate board feet from log volume

If you want a quick gross estimate, treat the log like a cylinder. Measure the small-end diameter inside bark in inches, convert the circular cross section into area, multiply by log length in feet, and convert cubic feet to board feet. The calculator above uses this formula for the cylindrical estimate:

Cylindrical board feet = π × diameter² × length ÷ 48

In this formula, diameter is in inches and length is in feet. This method is easy and mathematically clean, but it usually overstates usable lumber because it ignores taper, slabs, kerf, sweep, rot, and other deductions. In other words, it estimates wood volume, not finished lumber recovery.

The three most common log scale rules

Most timber transactions use a log rule rather than raw cylindrical volume. A log rule is a practical estimate of how many board feet of lumber a log can produce. The three classic rules in the United States are Doyle, Scribner, and International 1/4-inch. Each one gives a different answer from the same log because each one assumes different waste patterns and sawing conditions.

1. Doyle rule: Common in many hardwood regions. It tends to underestimate volume in smaller logs and becomes more favorable as diameters increase.
2. Scribner rule: Based on diagrammed board layouts. It often gives a middle-ground estimate, though it still has limitations with taper and modern saw kerf.
3. International 1/4-inch rule: Widely regarded as more consistent across log sizes because it models taper and a 1/4-inch kerf more realistically.

The calculator above uses practical forms of these formulas:

• Doyle: ((D – 4)² × L) ÷ 16
• Scribner: ((0.79 × D²) – (2 × D) – 4) × (L ÷ 16)
• International 1/4-inch: ((0.22 × D²) – (0.71 × D)) × (L ÷ 4)

Here, D is the small-end diameter inside bark in inches, and L is the log length in feet. These formulas are useful estimating tools, especially when you need a fast comparison.

How to measure a log for board feet

Accurate board foot estimation starts with careful measurement. A bad diameter reading or wrong length can change the estimate enough to affect pricing. Follow these steps:

1. Measure the small-end diameter inside bark. This is the preferred diameter for most log rules because the narrow end limits the lumber that can be sawn from the log.
2. Measure the log length in feet. Many scales assume standard lengths such as 8, 10, 12, 14, or 16 feet. If there is trim allowance, note whether your local buyer includes it.
3. Inspect the log for defects such as rot, sweep, crook, cracks, shake, or excessive knots. Apply a defect deduction if needed.
4. Choose the log rule used in your market. This is crucial because two buyers can look at the same log and produce different board foot totals using different scales.

Why the same log can have different board foot values

A common source of confusion is that there is no single board foot answer for every log. For example, a 16-inch diameter, 16-foot log produces very different estimates depending on the method you use. Cylindrical volume gives the gross wood content. Doyle usually gives the lowest estimate in smaller logs. International 1/4-inch often gives the highest sawlog estimate among the classic rules. None of these methods is automatically “wrong.” They answer slightly different questions.

16-foot log, small-end diameter	Doyle estimate	Scribner estimate	International 1/4-inch estimate	Cylindrical volume estimate
12 inches	64 bf	85.8 bf	92.6 bf	150.8 bf
16 inches	144 bf	166.2 bf	179.8 bf	268.1 bf
20 inches	256 bf	272.0 bf	323.6 bf	418.9 bf
24 inches	400 bf	428.0 bf	495.4 bf	603.2 bf

This comparison shows why scale selection matters. If your local market buys hardwood sawlogs on the Doyle scale, using cylindrical volume would dramatically overestimate what you should expect to be paid for. If you are only estimating physical wood content for shop planning, cylindrical volume may still be useful, but it is not the same thing as recoverable lumber.

Worked example: calculating board feet in one log

Suppose you have a log that is 16 feet long with a 16-inch small-end diameter inside bark. Here is how the estimates compare:

• Doyle: ((16 – 4)² × 16) ÷ 16 = 144 board feet
• Scribner: ((0.79 × 256) – 32 – 4) × (16 ÷ 16) = 166.24 board feet
• International 1/4-inch: ((0.22 × 256) – (0.71 × 16)) × (16 ÷ 4) = 179.84 board feet
• Cylindrical volume: π × 16² × 16 ÷ 48 = 268.08 board feet

If the log has a 10 percent defect deduction, multiply the chosen result by 0.90. Under Doyle, that would reduce the net estimate to 129.6 board feet. This is why defect deductions matter in real-world scaling. A straight, sound log and a rotten, sweepy log of the same dimensions should not be valued the same way.

Understanding inside bark versus outside bark

One of the most common beginner mistakes is measuring outside the bark and plugging that number directly into a board foot formula. Bark adds thickness that does not become usable lumber. Most log rules are based on diameter inside bark, or on local scaling conventions that effectively account for bark. If you only have outside-bark diameter, ask your buyer or forester how bark deduction is handled in your area. Even a one-inch error in diameter can change the estimate noticeably.

Why log length changes value

Longer logs are not always linearly better. In theory, increasing length increases volume, but in practice length interacts with taper, defects, market requirements, and trim. A 16-foot straight log may scale better than two short defect-heavy segments, or the reverse may be true if a long log contains a crook or seam that ruins grade. That is why professional log scaling is both a math task and a quality assessment.

Diameter	Length	Cubic feet	Equivalent gross board feet	Board foot fact
12 inches	8 feet	6.28 cu ft	75.4 bf	1 board foot = 144 cubic inches
16 inches	12 feet	16.76 cu ft	201.1 bf	1 board foot = 1/12 cubic foot
18 inches	16 feet	28.27 cu ft	339.3 bf	Gross volume exceeds sawn recovery
24 inches	10 feet	31.42 cu ft	377.0 bf	Scale rules reduce this to realistic yield

When should you use each method?

Use a cylindrical volume estimate if you are interested in raw log volume or want a quick physical benchmark. Use Doyle if that is the standard in your local timber market. Use Scribner if your buyer or mill quotes Scribner scale. Use International 1/4-inch when you want a more balanced estimate of lumber recovery across a wider range of diameters. In all cases, the best answer is the one that matches the market or operational standard you actually have to work with.

Common mistakes when calculating board feet in a log

• Using outside-bark diameter instead of inside-bark diameter
• Mixing inches and feet without converting correctly
• Ignoring defect deductions
• Comparing logs scaled under different rules as if they were equal
• Assuming gross geometric volume equals recoverable lumber yield
• Rounding too early in the process

Board foot estimates versus actual lumber recovery

Even the best board foot estimate is still an estimate. Actual recovery depends on species, taper, sweep, knots, butt flare, internal defects, saw kerf, mill equipment, sawing pattern, operator skill, and final target products. A high-quality veneer or grade sawlog may produce much more value than a low-grade log with the same board foot scale. That is why board footage is only one part of log appraisal. Grade and end use often matter just as much.

Practical advice for landowners and woodworkers

If you are a landowner selling timber, ask the buyer which scale they use and how defects are deducted. If you are a sawyer or woodworker buying logs privately, compare at least two rules before negotiating price so you understand the spread. If you are milling for your own use, keep a record of actual lumber recovery from logs of known diameters and species. Over time, your own recovery data may become even more valuable than published scale tables because it reflects your actual equipment and sawing practice.

Authoritative resources for deeper study

For official and university-based references on log rules, timber measurement, and wood volume, review these sources:

• Penn State Extension: Forest measurement and volume estimation
• University of Missouri Extension: Measuring standing timber and logs
• USDA Forest Service: Forestry measurement and timber resources

Final takeaway

So, how do you calculate board feet in a log? Start by measuring the small-end diameter inside bark and the log length. Then apply the correct method for your purpose. For raw wood content, use a cylindrical volume formula. For sawlog estimation, use Doyle, Scribner, or International 1/4-inch, depending on your market. Finally, subtract any defect deduction to arrive at a more realistic net figure. The calculator on this page lets you do all of that quickly, while also showing how much the answer changes when you switch scaling rules. That comparison is often the most important insight of all.