log board feet calculator

Accurately estimate the lumber yield of your logs using the industry-standard Doyle, Scribner, and International 1/4-inch log rules. Essential for loggers, sawyers, and timber buyers.

Formula Note: Calculations assume standard taper and sound logs. Actual yield may vary based on kerf width and log defects.

What is a Log Board Feet Calculator?

A Log Board Feet Calculator is a specialized tool used by foresters, sawyers, and timber owners to estimate the volume of usable lumber that can be sawn from a raw log. In the timber industry, volume is measured in "board feet" (BF), where one board foot represents a piece of lumber 12 inches wide, 12 inches long, and 1 inch thick.

Who should use this tool? Anyone involved in the lifecycle of timber—from landowners selling standing trees to hobbyist woodworkers milling their own logs. Using a Log Board Feet Calculator helps ensure fair pricing during transactions and allows for efficient planning of construction projects. A common misconception is that all log rules provide the same result; in reality, different mathematical models (Doyle, Scribner, and International) can produce significantly different estimates for the same log.

Log Board Feet Calculator Formula and Mathematical Explanation

The math behind a Log Board Feet Calculator depends on which "rule" is applied. Each rule was developed at a different time in history to account for saw kerf (the width of the saw blade cut) and slab waste.

1. Doyle Log Rule

The Doyle rule is one of the oldest and most widely used in the Eastern United States. It is known for underestimating small logs and overestimating large ones.

Formula: BF = ((D - 4) / 4)² × L

2. International 1/4-Inch Rule

This is considered the most accurate rule for modern sawmills because it accounts for log taper and a standard 1/4-inch saw kerf.

Formula (for 4ft sections): BF = (0.22D² - 0.71D) (Calculated in 4-foot segments with 1/2 inch taper added per segment).

3. Scribner Decimal C Rule

The Scribner rule is based on diagrams of boards drawn inside circles. It does not account for taper, making it conservative for long logs.

Variables used in Log Board Feet Calculator

Variable	Meaning	Unit	Typical Range
D	Small End Diameter	Inches	6″ – 40″
L	Log Length	Feet	8′ – 24′
BF	Board Feet	Board Foot	10 – 2000+
Kerf	Saw Blade Width	Inches	1/8″ – 1/4″

Practical Examples (Real-World Use Cases)

Example 1: Small Pine Log
Suppose you have a pine log that is 12 feet long with a small-end diameter of 10 inches. Using the Log Board Feet Calculator:
– Doyle: 27 BF
– Scribner: 30 BF
– International 1/4″: 40 BF
In this case, the Doyle rule significantly penalizes the small diameter, while the International rule provides a more realistic yield for a modern thin-kerf bandsaw.

Example 2: Large Oak Log
Consider a massive oak log 16 feet long and 24 inches in diameter:
– Doyle: 400 BF
– Scribner: 400 BF
– International 1/4″: 425 BF
For larger logs, the rules tend to converge, though International still accounts for the taper gain over the 16-foot length.

How to Use This Log Board Feet Calculator

1. Measure the Length: Determine the length of the log in feet. If the log is 16 feet 4 inches, round down to 16 feet (the extra is "trim").
2. Measure the Diameter: Measure the diameter inside the bark at the small end of the log. If the log is oval, take two measurements at right angles and average them.
3. Select Your Rule: Choose the log rule used in your region or by your local sawmill.
4. Analyze Results: The Log Board Feet Calculator will instantly show the estimated yield. Use the "Copy Results" button to save the data for your records.
5. Decision Making: If you are selling timber, compare the Doyle and International results to understand how much volume you might be "giving away" if the buyer uses a conservative rule.

Key Factors That Affect Log Board Feet Calculator Results

• Log Taper: The International rule accounts for the fact that logs get wider toward the base. Rules that ignore taper (like Scribner) will underestimate volume on long logs.
• Saw Kerf: The width of the saw blade determines how much wood is turned into sawdust. The International 1/4″ rule assumes a 0.25-inch kerf.
• Log Defects: No Log Board Feet Calculator can account for internal rot, knots, or "sweep" (curves in the log) without manual deductions.
• Slab Waste: The outer "slabs" of a log are discarded. The formulas include a built-in reduction to account for this loss.
• Scaling Practice: "Scaling" is the art of measuring. Small errors in diameter measurement (e.g., including bark) can lead to large errors in volume calculation.
• Species Variation: While the math is geometric, some species produce more usable lumber due to straighter growth patterns.

Frequently Asked Questions (FAQ)

Which log rule is the most accurate?

The International 1/4-Inch rule is widely considered the most mathematically accurate for modern sawmills as it accounts for both taper and kerf.

Why does the Doyle rule give such low numbers for small logs?

The Doyle rule subtracts 4 inches from the diameter to account for slabs and kerf. For a 6-inch log, this leaves only 2 inches of "usable" wood in the formula, which is an excessive reduction.

Should I measure diameter with or without bark?

Always measure inside the bark (DIB). The bark does not produce lumber and should not be included in the Log Board Feet Calculator input.

What is "overrun"?

Overrun occurs when a sawmill actually produces more lumber than the Log Board Feet Calculator predicted. This is common when using the Doyle rule on small logs.

How do I handle logs longer than 20 feet?

Most scalers treat very long logs as two separate shorter logs to better account for taper and maintain accuracy.

Does the calculator account for wood density?

No, board feet is a measure of volume, not weight. For weight, you would need a separate species-specific density chart.

What is a "Board Foot"?

It is a unit of volume equal to 144 cubic inches (12″ x 12″ x 1″).

Can I use this for standing trees?

This calculator is for felled logs. For standing trees, you need a "Tree Scale" rule which accounts for usable log height and DBH (diameter at breast height).