How to Calculate Board Feet From a Log
Estimate lumber yield fast with this premium log scale calculator. Enter the small-end diameter, log length, choose a log rule, and compare Doyle, Scribner, and International 1/4-inch outputs instantly.
Log Board Foot Calculator
Measure inside bark if possible for the best estimate.
Common sawlog lengths include 8, 10, 12, 14, and 16 feet.
Estimated yield
Results will show your selected rule, a comparison across major log rules, and a chart for quick interpretation.
Expert Guide: How to Calculate Board Feet From a Log
Learning how to calculate board feet from a log is one of the most useful skills in forestry, sawmilling, logging, and hardwood buying. Whether you are a woodland owner pricing timber, a portable sawmill operator estimating yield, or a buyer comparing loads, board foot calculations help convert a round log into a practical estimate of lumber volume. The key point is that a log is not sold or processed as simple cubic volume alone. Instead, many parts of the wood industry use log rules that estimate how many board feet of lumber can be sawn from the log after accounting for slab loss, saw kerf, and the geometry of turning a cylinder into boards.
A board foot is a unit of lumber volume equal to a board that is 12 inches long, 12 inches wide, and 1 inch thick. That equals 144 cubic inches. For sawn lumber, the math is straightforward: thickness in inches multiplied by width in inches multiplied by length in feet, divided by 12. Logs are different. Since a standing or bucked log is round and tapered, you need a log scale rule to estimate board feet. The most common rules in North America are Doyle, Scribner, and International 1/4-inch. Each gives a different answer for the same log because each assumes a different level of waste and saw kerf.
The basic information you need
To estimate board feet from a log accurately, you usually need only two primary measurements and one rule choice:
- Small-end diameter, usually measured inside bark in inches
- Log length, usually measured in feet
- Log scale rule, such as Doyle, Scribner, or International 1/4-inch
Most buyers and scalers measure at the small end because that is the limiting dimension for sawing boards through the full length of the log. If your diameter is measured outside bark instead of inside bark, the estimate can run high. Bark thickness varies by species and age, so inside-bark scaling is generally preferred whenever possible.
Step-by-step: the easiest way to calculate board feet from a log
- Measure the diameter at the small end of the log.
- Measure the usable length of the log.
- Select the rule used by your buyer, mill, forester, or local market.
- Apply the formula or use a scale table.
- Compare estimates if you are negotiating a sale or planning production.
For example, if a log is 18 inches in diameter at the small end and 16 feet long, the estimated yield changes depending on the rule used. A Doyle estimate is usually lower for smaller logs, while International 1/4-inch often produces a higher figure because it is designed to more closely reflect modern sawing efficiency.
Common formulas used in practice
There are different versions of log tables and scaling conventions, but the following simplified formulas are widely used for estimating board feet:
- Doyle: ((D – 4) × (D – 4) × L) ÷ 16
- Scribner: ((0.79 × D²) – (2 × D) – 4) × (L ÷ 16)
- International 1/4-inch: ((0.905 × D²) – (1.221 × D) – 0.719) × (L ÷ 16)
In these formulas, D is small-end diameter in inches and L is log length in feet. These formulas produce estimated board feet, not actual guaranteed output. Real-world recovery depends on taper, sweep, defects, species, sawing pattern, and target product dimensions.
Worked example
Suppose you have a 16-foot log with a small-end diameter of 20 inches:
- Doyle: ((20 – 4)² × 16) ÷ 16 = 256 board feet
- Scribner: ((0.79 × 400) – 40 – 4) × (16 ÷ 16) = 272 board feet
- International 1/4-inch: ((0.905 × 400) – 24.42 – 0.719) × 1 = about 337 board feet
This example highlights why rule selection matters. If a timber owner assumes International 1/4-inch values but the local market pays on Doyle scale, the expected revenue can differ significantly. That is why serious log buying and selling should always specify the scaling rule in writing.
Comparison table: same log, different rule
| Small-end diameter | Length | Doyle estimate | Scribner estimate | International 1/4-inch estimate |
|---|---|---|---|---|
| 14 in | 12 ft | 75 bf | 90 bf | 120 bf |
| 16 in | 16 ft | 144 bf | 166 bf | 212 bf |
| 18 in | 16 ft | 196 bf | 216 bf | 271 bf |
| 20 in | 16 ft | 256 bf | 272 bf | 337 bf |
| 24 in | 16 ft | 400 bf | 403 bf | 491 bf |
The values above illustrate a common market reality: Doyle tends to under-scale smaller logs more sharply than International 1/4-inch. As diameter increases, some of the differences narrow, but they do not disappear. This is one reason landowners are encouraged to understand local scaling practices before selling timber.
What makes board foot estimates change?
Even if two logs have the same measured diameter and length, actual sawmill recovery can differ. Here are the biggest factors:
- Taper: A log narrows from butt to top, and more taper usually lowers recovery.
- Sweep and crook: Curved logs create more waste during sawing.
- Defects: Rot, checks, seams, knots, and metal all reduce usable lumber.
- Species: Bark thickness, sawing strategy, and target products vary by species.
- Saw kerf: Thin-kerf bandsaws waste less wood than wider circular saws.
- Mill optimization: Modern scanning systems can improve actual lumber recovery.
Why the Doyle rule often feels conservative
The Doyle rule is still common in parts of the United States, especially in hardwood markets, because it is familiar and historically established. However, it was developed for older sawing technology with wider kerf assumptions. It tends to underestimate board feet in small and medium logs. That does not make it wrong in a market sense if everyone uses Doyle, but it does mean it may not closely match what a modern portable band mill or optimized headrig can recover.
Why International 1/4-inch is often closer to modern recovery
International 1/4-inch was designed to account more realistically for taper and a thinner saw kerf. For many modern operations, especially where accurate yield planning matters, it is often considered a better technical estimate than Doyle. In practice, though, the “best” rule is still the one your transaction or procurement agreement specifies.
Field measurement best practices
- Use a diameter tape or logger’s tape for consistency.
- Measure the small-end diameter inside bark whenever practical.
- Measure log length to the nearest standard allowance used in your market.
- Separate logs by grade and species instead of averaging everything together.
- Document your rule, units, and assumptions before quoting a value.
Comparison table: rule behavior by log size
| Log size category | Doyle behavior | Scribner behavior | International 1/4-inch behavior | Typical practical takeaway |
|---|---|---|---|---|
| Small logs under 14 in | Often notably low | Moderate estimate | Usually highest of the three | Rule choice can materially change value per log |
| Medium logs 14 to 20 in | Still conservative | Common middle-ground estimate | Often closer to modern mill recovery | Always confirm which rule the buyer uses |
| Large logs over 20 in | Differences narrow somewhat | Competitive estimate | Still usually higher | Grade and defect often matter more than rule alone |
How board foot estimates relate to cubic volume
Some new woodland owners confuse board feet and cubic feet. They are not the same. Cubic measures describe the total solid wood volume, while board feet are an estimate of recoverable lumber product. A perfect cylinder can have a certain cubic volume, but the amount of lumber you can actually saw from it depends on board dimensions, saw kerf, edging, trimming, defects, and slab loss. That is exactly why log rules were created. They translate a round log into a practical lumber estimate.
When to use a board foot calculator
- Before selling sawlogs from private timberland
- When planning portable sawmill jobs
- For rough budgeting of lumber yield from felled trees
- To compare buyer quotes using different scaling rules
- When teaching forestry, wood products, or log scaling fundamentals
Common mistakes to avoid
- Using outside-bark diameter without adjustment
- Measuring the large end instead of the small end
- Forgetting to state the scaling rule
- Comparing log prices from different rules as if they were equivalent
- Assuming estimated board feet equals actual dried, surfaced lumber output
Useful authoritative references
If you want deeper background on timber measurement, scaling, and forest product marketing, consult these sources:
- Penn State Extension: Forest measurement and volume estimation
- University of Minnesota Extension: Measuring trees and logs
- U.S. Forest Service: Forest products and timber measurement resources
Final takeaway
To calculate board feet from a log, measure the small-end diameter, measure the length, and apply the log rule used in your market. Doyle, Scribner, and International 1/4-inch are all valid scaling systems, but they do not produce the same answer. For landowners, sawyers, and buyers, the smartest approach is to calculate all three, understand the difference, and verify which rule controls the transaction. Use the calculator above to estimate yield instantly and compare the major log rules side by side before you price, buy, or mill a log.