Calculate Board Feet in a Log
Estimate lumber yield from a single log using three common log rules: Doyle, Scribner, and International 1/4-inch. Enter the small-end diameter, log length, quantity, and scale rule to get an instant board foot estimate and a visual comparison chart.
Log Board Foot Calculator
Doyle: ((D – 4)² × L) / 16
Scribner: ((0.79 × D²) – (2 × D) – 4) × (L / 16)
International 1/4-inch: ((0.199 × D²) – (0.642 × D) – 1) × L
Expert Guide: How to Calculate Board Feet in a Log
Board foot estimation is one of the most practical skills in sawmilling, timber buying, woodland management, and custom lumber planning. If you need to calculate board feet in a log, you are really trying to estimate how much usable lumber a round log can produce after it is sawn into boards. A board foot is a unit of lumber volume equal to a piece that is 1 inch thick, 12 inches wide, and 12 inches long. That means a 2 inch by 6 inch board that is 8 feet long contains 8 board feet, because its volume equals 96 cubic inches divided by 144.
When you estimate board feet in standing timber or felled logs, you usually do not calculate directly from true cylinder volume. Instead, you use a log rule. A log rule is a formula or table created to estimate lumber output after accounting for slab loss, saw kerf, taper, and practical cutting limitations. The three most common rules in North America are the Doyle rule, the Scribner rule, and the International 1/4-inch rule. Each uses a different assumption about how much wood turns into lumber, so each can produce a different number for the same log.
What a board foot means in practical forestry
Board feet matter because log buyers, sawmills, woodlot owners, and portable mill operators often use them for valuation and production planning. If a hardwood log is estimated at 250 board feet and the local delivered log value is $0.70 per board foot, the gross estimate is about $175. If you are planning a barn, timber frame, live-edge slab inventory, or a custom furniture run, board foot estimates also help you decide whether a log pile is large enough for the project.
It is important to understand that a board foot estimate is not the same as guaranteed finished yield. Real recovery can change due to sweep, crook, internal defects, heart shake, species characteristics, machine setup, sawing pattern, and target product sizes. In other words, board foot scaling is an estimate, but it is still the standard language used in many timber and log transactions.
The measurements you need
To calculate board feet in a log with a scale rule, you generally need these inputs:
- Small-end diameter inside bark: This is the diameter at the narrow end of the log after excluding bark. Many standard rules are based on small-end diameter.
- Log length: Usually measured in feet. Some traditional scale methods use even-foot or standard-log lengths.
- Log count: If you have multiple logs of similar size, you can multiply the result.
- Scale rule: Doyle, Scribner, or International 1/4-inch.
If you are measuring in the field, use a log scale stick or a diameter tape for the diameter and a logger’s tape for length. Be consistent about whether bark is included. If the local buyer scales inside bark, entering outside-bark measurements can overestimate volume.
How the three main log rules differ
The main reason two buyers or two calculators can give different board foot estimates is that they may be using different rules. Here is the practical difference:
- Doyle: Often underestimates small logs and is most favorable to larger diameters. It is still widely used in some hardwood markets.
- Scribner: Based on a geometric board layout concept. It is often seen as a middle-ground traditional rule.
- International 1/4-inch: Often considered the most consistent and realistic of the three because it better accounts for taper and saw kerf over a range of sizes.
| Scale Rule | Typical Behavior | Strength | Common Limitation |
|---|---|---|---|
| Doyle | Conservative on small logs, more generous on large logs | Common in some hardwood markets and easy to recognize | Can significantly undervalue small-diameter logs |
| Scribner | Moderate estimate with historical saw pattern assumptions | Widely referenced in timber scaling | Less precise than International for some log sizes |
| International 1/4-inch | Usually higher and more consistent on small to medium logs | Often viewed as a more realistic technical estimate | May differ from the local buyer’s preferred market rule |
Sample comparison using common log sizes
To show why the selected rule matters, the table below compares estimated board feet for several representative logs using standard formulas. The numbers are approximate and will vary with local scaling conventions, but they clearly show the pattern: Doyle tends to lag for smaller diameters, while International 1/4-inch usually returns the highest estimate in that range.
| Small-End Diameter | Length | Doyle BF | Scribner BF | International 1/4-inch BF |
|---|---|---|---|---|
| 12 in | 16 ft | 64 | 86 | 120 |
| 16 in | 16 ft | 144 | 166 | 223 |
| 20 in | 16 ft | 256 | 272 | 321 |
| 24 in | 16 ft | 400 | 404 | 445 |
These values are formula-based examples intended for comparison. Actual mill scale can vary due to trim allowances, defect deductions, local practice, and whether the diameter is recorded inside bark or outside bark.
Step-by-step method to calculate board feet in a log
- Measure the log length in feet. Be precise, especially on short logs. Log buyers may scale in standard increments.
- Measure the small-end diameter inside bark. This is the most common reference point for scale rules.
- Choose the correct scale rule. Use the one accepted by your mill, buyer, state guidance, or management plan.
- Apply the formula or scale table. The calculator above does this instantly.
- Multiply by the number of similar logs. If your pile is mixed, calculate each size class separately.
- Optionally estimate value. Multiply total board feet by your expected price per board foot.
Why actual sawmill yield can differ from scaled board feet
Many first-time users assume that if a log scales 300 board feet, the sawmill will always produce exactly 300 board feet of lumber. In reality, scale is an estimate tied to a rule, not a perfect guarantee of output. Actual recovery depends on factors such as:
- Species and growth form
- Knots, decay, and internal defects
- Crook, sweep, butt flare, or taper
- Saw kerf width and machine type
- Whether the goal is grade lumber, timbers, or live-edge slabs
- Trim loss and moisture-related shrinkage
A skilled sawyer can often improve practical recovery by orienting defects strategically or selecting a sawing pattern that fits the market. For example, quarter sawing, grade sawing, and cant sawing may produce very different product mixes from the same log. That is why a board foot estimate is most useful as a planning and comparison tool rather than as an exact finished-lumber guarantee.
Using board foot estimates in timber sales
In timber transactions, knowing how to calculate board feet in a log helps you compare offers and understand bid sheets. If a buyer uses Doyle and another quotes in Scribner or International, the number alone is not enough. You have to compare both the rule and the price. A lower board foot estimate with a higher rate can sometimes equal or exceed the value of a higher estimate with a lower rate.
For private woodland owners, this is one reason extension foresters and consulting foresters often recommend documenting the scale rule used in every conversation and contract. A board foot is not a universal number unless everyone is using the same rule under the same assumptions.
Common mistakes when measuring logs
- Using outside-bark diameter when the rule expects inside bark.
- Rounding the diameter too aggressively. A one-inch difference can noticeably change the result.
- Ignoring trim or merchantable length standards.
- Assuming one scale rule is interchangeable with another.
- Applying a formula to unusually short, highly tapered, or defective logs without field judgment.
Good scaling combines measurement discipline with practical experience. If the log is badly flared, hollow, or curved, a straightforward formula may not tell the full story.
Authoritative resources for log measurement and scaling
If you want official guidance, extension publications and federal forestry resources are excellent references. These sources are particularly helpful for field methods, scaling conventions, and timber sale education:
When to use each scale rule
If you are milling your own logs for project planning, International 1/4-inch often gives a technically useful benchmark because it reflects sawing losses more realistically across many diameters. If you are selling logs into a regional hardwood market that commonly uses Doyle, however, the market rule is usually the one that matters most for pricing. Scribner remains important in some historical and regional contexts and is still commonly referenced. The correct choice is not just the mathematically nicest formula. It is the rule that aligns with the transaction or planning goal.
Final takeaways
To calculate board feet in a log, measure the small-end diameter, record the merchantable length, select the log rule, and apply the appropriate formula. The calculator above simplifies the process and also shows a side-by-side comparison among Doyle, Scribner, and International 1/4-inch so you can see how rule selection changes the estimate. That comparison is often just as valuable as the final number, especially when you are discussing log values, comparing bids, or deciding whether a group of logs is worth milling.
Used correctly, board foot scaling helps bring consistency to forestry decisions, sawmill planning, and lumber valuation. It is not a substitute for grading or hands-on experience, but it is one of the most essential measurement tools in the wood products world.