Calculating Board Feet In A Log

Estimate lumber yield from a log using widely recognized log rules. Enter the small-end diameter inside bark, log length, and scaling rule to calculate board feet instantly and compare results across Doyle, Scribner, and International 1/4-inch methods.

Expert Guide to Calculating Board Feet in a Log

Calculating board feet in a log is one of the most practical skills in forestry, sawmilling, log buying, woodland management, and timber sales. A board foot is a unit of lumber volume equal to a board that measures 1 inch thick, 12 inches wide, and 12 inches long. In simple terms, that is 144 cubic inches of wood. However, when you are estimating yield from an entire round log, the answer is not as straightforward as measuring a cylinder and converting volume. Real log scaling systems account for slab loss, saw kerf, taper, and the practical limitations of turning a round stem into rectangular boards.

That is why foresters, sawyers, and timber buyers rely on log rules rather than raw geometric volume alone. A log rule is a formula or table used to estimate how many board feet of sawn lumber can be recovered from a log of a specific diameter and length. In the United States, the three most common rules are the Doyle Rule, the Scribner Rule, and the International 1/4-inch Rule. Each one produces a different estimate because each is based on different assumptions about saw kerf, taper, and mill efficiency.

This calculator helps you estimate board feet using all three methods while letting you choose the primary rule that matters for your sale, appraisal, or milling plan. Understanding how these rules work can help you price logs more accurately, compare buyer bids fairly, and make better woodland management decisions.

What a Board Foot Means in Log Scaling

A board foot is not the same as a cubic foot. Board foot measurements are intended to estimate the amount of lumber that can be sawn from a log, not the total solid wood content of the log. Two logs with similar cubic volume can produce different lumber yields if one has more taper, sweep, crook, rot, or defects. Log rules are therefore best viewed as standardized yield estimates, not perfect predictions.

The standard board foot definition

• 1 board foot = 1 inch thick × 12 inches wide × 12 inches long
• Equivalent solid volume = 144 cubic inches
• 12 board feet = 1 cubic foot of finished board volume in theory
• Actual sawmill recovery depends on kerf, edging, trimming, defects, and equipment

When someone says a log scales 250 board feet, they typically mean that according to a particular log rule, the log is estimated to yield about 250 board feet of lumber. The same log might scale differently under another rule.

The Three Main Log Rules

1. Doyle Rule

The Doyle Rule is widely used in parts of the eastern and southern United States. It is simple and historically popular, but it tends to underestimate the yield of small logs and becomes more favorable as log diameter increases. Its common formula is:

Doyle board feet = ((D – 4)² × L) ÷ 16

Where D is the small-end diameter inside bark in inches, and L is log length in feet. Because it subtracts 4 inches from the diameter before squaring, smaller logs can scale surprisingly low.

2. Scribner Decimal C Rule

The Scribner Rule is based on a diagram method that estimates how boards can be cut from a log cross section. In practice, many calculators use the Scribner Decimal C approximation. It generally gives moderate results and is commonly used in western and some central markets.

Scribner Decimal C approximation = ((0.79 × D²) – (2 × D) – 4) × L ÷ 16

This method often produces estimates higher than Doyle on smaller logs, but it still has limitations because it is based on simplified assumptions about board layout.

3. International 1/4-inch Rule

The International 1/4-inch Rule is widely regarded as the most consistent of the three for estimating actual lumber recovery because it includes assumptions for taper and a 1/4-inch saw kerf. It usually produces higher estimates than Doyle and often somewhat higher than Scribner, especially on smaller to medium logs.

The calculator uses a standard equation-based approximation commonly applied in forestry references for this rule. Because it better reflects sawing realities, many foresters consider it a strong choice for comparing logs across a broad range of sizes.

Important: Always verify which log rule a buyer, mill, consulting forester, or timber sale contract uses. A price that sounds higher under one rule may not actually be better if another buyer is scaling logs under a different rule.

How to Calculate Board Feet in a Log Step by Step

1. Measure the small-end diameter inside bark. This is the scaling diameter used in most log rules. Bark thickness should not be included unless your market specifically says otherwise.
2. Measure merchantable log length. Typical sawlog lengths are 8 to 16 feet, sometimes with trim allowances. Use the actual length expected to be scaled.
3. Select the log rule. Choose Doyle, Scribner, or International 1/4-inch based on your region or transaction.
4. Apply the formula or use a scale table. The calculator automates this step instantly.
5. Review results across all rules. Comparing methods can reveal how strongly rule selection affects value.

Worked Example

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

• Doyle: ((20 – 4)² × 16) ÷ 16 = 256 board feet
• Scribner: ((0.79 × 20²) – (2 × 20) – 4) × 16 ÷ 16 = 272 board feet
• International 1/4-inch: using the standard approximation, the estimate is higher, reflecting more realistic recovery assumptions for many sawing conditions

Even in this simple case, the same log can produce meaningfully different scale values depending on the rule used. This is why contract language and buyer communication matter.

Comparison Table: Estimated Board Feet by Rule

The table below shows example estimates for common log sizes. Values are representative calculations using the same formulas used by this calculator, rounded to whole board feet.

Small-end diameter inside bark	Length	Doyle Rule	Scribner Rule	International 1/4-inch Rule
12 inches	8 feet	32 bf	43 bf	52 bf
16 inches	12 feet	108 bf	128 bf	150 bf
20 inches	16 feet	256 bf	272 bf	315 bf
24 inches	16 feet	400 bf	403 bf	463 bf
28 inches	16 feet	576 bf	572 bf	648 bf

The trend is clear: Doyle is notably conservative on smaller logs, while International 1/4-inch tends to produce the highest estimate. As diameter increases, Doyle begins to narrow the gap, and in some cases Doyle and Scribner become fairly close.

Real-World Statistics and Why Recovery Varies

Log rules are standardized estimates, but actual sawmill output can differ. Recovery depends on saw kerf width, taper, straightness, species, defect, target lumber dimensions, and mill technology. Modern thin-kerf bandsaw systems can often recover more lumber than older circular saw operations, especially from small logs.

Factor affecting actual yield	Typical effect on lumber recovery	Practical implication
Saw kerf width	Thin-kerf systems may improve recovery by several percentage points compared with wider kerf setups	Actual yield can exceed older rule assumptions
Small log diameter	Recovery is lower because slabs and edging consume a larger share of volume	Doyle especially underestimates small logs
Taper and sweep	More taper reduces recoverable rectangular lumber	Scaling based only on one diameter may overstate usable lumber
Internal defect	Rot, shake, stain, and knots can sharply reduce value and grade	Board foot scale is not the same as board foot value
Mill technology	Optimization software and scanning can improve recovery over traditional methods	Two mills may recover different volumes from the same log

Forestry research and extension publications routinely note that the choice of scaling system can change reported volume significantly. This is particularly important in timber sales, where a different scale rule can influence both per-log estimates and total tract volume. That is one reason professional foresters document not only species and grade, but also the exact scaling method used.

Common Mistakes When Estimating Board Feet

• Measuring outside bark instead of inside bark. Bark can add enough thickness to overstate board foot volume.
• Using the wrong diameter point. Most rules use the small-end diameter of the merchantable log.
• Ignoring trim allowance. If the log is cut with trim, confirm whether the market scales net or gross length.
• Comparing prices without comparing rules. A higher dollar rate under Doyle may not beat a lower rate under International 1/4-inch if the scale volume differs sharply.
• Assuming scale equals value. Species, grade, defects, and current market demand can matter as much as gross board foot volume.

How Professionals Use Board Foot Calculations

Board foot estimates are used in many settings:

• Standing timber sales and bid comparisons
• Truckload verification at receiving yards
• Sawmill production planning
• Woodland inventories and management plans
• Estimating project lumber supply from private logs
• Appraisals, insurance documentation, and storm damage assessments

If you are a landowner, the most valuable habit is consistency. Measure logs carefully, use one recognized rule for comparison, and note the assumptions used. If you are selling timber, ask the buyer to state the scaling method in writing. If you are milling your own logs, compare scale estimates with actual lumber output over time. Doing that creates a practical benchmark for your species mix and equipment.

Authoritative Forestry Sources

If you want to go deeper into log rules, scaling, and timber measurement, these public resources are excellent starting points:

• U.S. Forest Service for forestry guidance, forest products research, and timber measurement references.
• Penn State Extension for wood products conversion guidance and forestry education resources.
• Purdue Extension Forestry and Natural Resources for practical educational materials on log volume, timber measurements, and woodland management.

Which Rule Should You Use?

There is no single universal answer. Use the rule standard in your region or the rule specified in your transaction. If your goal is to estimate likely sawn lumber recovery, International 1/4-inch is often preferred because it more closely reflects sawing realities across a broad range of diameters. If your local market buys and sells under Doyle, then Doyle is the practical answer because that is how value is being assigned. Scribner remains common and useful in many areas, especially where it is already built into log buying systems and historical records.

Final Takeaway

Calculating board feet in a log is both a math task and a market task. The math part involves diameter, length, and the chosen rule. The market part involves understanding what your buyer, forester, or sawmill actually uses. This calculator gives you both the selected result and a side-by-side comparison so you can make informed decisions quickly. For the most reliable outcomes, measure carefully, verify the scale method, and treat board foot volume as an estimate of yield rather than a guarantee of final lumber output.

This calculator provides an estimate for planning and educational purposes. For timber sale contracts, appraisals, or regulated measurements, consult a professional forester, scaler, or buyer and confirm the specific rule and grading standards being applied.