Log Scaling Rules Explained: Doyle vs Scribner vs International 1/4

When buying standing timber or selling harvested tree logs to a sawmill, board foot yield is estimated using log scale rules. Unlike square lumber boards measured with a standard construction calculator, logs are cylindrical and tapered, requiring specialized scaling formulas.

The three dominant log scale rules used in North America are:

1. Doyle Log Rule
2. Scribner Decimal C Rule
3. International 1/4-Inch Rule

This guide breaks down the mathematics behind each formula and explains which rule yields the most accurate board foot estimation.

1. Doyle Log Rule

The Doyle Log Rule is the oldest and most widely used log scale rule in the central and eastern United States.

Doyle Formula

$$\text{Board Feet} = \left(\frac{D - 4}{4}\right)^2 \times L$$

Where:

• $D$ = Diameter inside bark at the small end of the log (inches)
• $L$ = Log length (feet)

Key Characteristic of Doyle

• Underscales small logs (under 28 inches in diameter) because it overestimates slab and kerf losses by deducting a fixed 4 inches for slab waste.
• Overscales very large logs (over 36 inches in diameter).

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2. Scribner Decimal C Log Rule

Developed by J.M. Scribner in 1846, the Scribner Log Rule uses diagrammatic drawings of log cross-sections to determine the maximum number of 1-inch boards that can be sawn from a log, assuming a 1/4-inch saw kerf.

Key Characteristic of Scribner

• Rounded to the nearest 10 board feet (Decimal C).
• Does not account for log taper along its length, slightly underestimating yields on long logs (16+ feet).

3. International 1/4-Inch Log Rule

Developed by Judson F. Clark in 1906, the International 1/4-Inch Rule is considered the most mathematically accurate log rule for modern commercial sawmills.

Formula Basis

It calculates volume in 4-foot log sections, incorporating:

• 1/4-inch saw kerf allowance
• 1/16-inch shrinkage factor
• Standard log taper of 1/2 inch per 4 feet of log length

$$\text{Board Feet} = 0.22 D^2 - 0.71 D \quad \text{(per 4 ft section)}$$

Log Rule Comparison Table (16-Foot Log)

Below is a comparison of estimated board footage for a 16-foot log across different small-end diameters:

Notice how Doyle significantly underestimates timber yield on smaller diameter logs (12” to 16”).

Frequently Asked Questions (FAQ)

Which log scale rule gives the highest board foot yield?

The International 1/4-Inch Rule provides the highest and most accurate board foot yield estimation for small to mid-sized sawlogs.

How do I calculate log board feet automatically?

Use our dedicated Log Scaling Calculator to instantly compare Doyle, Scribner, and International rules.

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