Doyle Scale Calculator

Doyle Log Scale Calculator

Measure the average diameter at the small end of the log, inside the bark.

Estimated Yield:

Based on the Doyle Log Rule formula.

function calculateDoyle() { var diameter = parseFloat(document.getElementById('logDiameter').value); var length = parseFloat(document.getElementById('logLength').value); var resultDiv = document.getElementById('doyleResult'); var output = document.getElementById('boardFeetOutput'); if (isNaN(diameter) || isNaN(length) || diameter <= 4 || length <= 0) { alert("Please enter valid positive numbers. Note: The Doyle rule requires a diameter greater than 4 inches."); resultDiv.style.display = 'none'; return; } // Doyle Formula: V = (D – 4)^2 * (L / 16) var boardFeet = Math.pow((diameter – 4), 2) * (length / 16); output.innerHTML = boardFeet.toFixed(2) + " Board Feet (bf)"; resultDiv.style.display = 'block'; }

Understanding the Doyle Log Scale

The Doyle Log Scale is one of the oldest and most widely used log scaling rules in the United States and Canada, particularly in the Southern and Midwestern states. It is designed to estimate the amount of usable lumber (measured in board feet) that can be sawn from a log of a specific diameter and length.

Loggers, sawmill operators, and timber buyers use this calculator to determine the volume of timber before it is processed. While newer scales like the Scribner or International 1/4-inch rule exist, the Doyle scale remains a standard in many private timber transactions.

The Doyle Scale Formula

The math behind the Doyle scale is relatively straightforward but has specific characteristics that benefit different parties depending on the log size. The formula is:

Board Feet = (Diameter – 4)² × (Length / 16)

• Diameter: Measured in inches at the small end of the log, inside the bark.
• Length: The length of the log measured in feet.
• The "Minus 4": This accounts for the slab allowance (the outer part of the log that becomes waste or chips).

When to Use This Calculator

It is important to understand "overrun" and "underrun" when using the Doyle rule:

• Small Logs: The Doyle scale tends to underestimate the volume of small logs. This results in an "overrun" for the sawmill, meaning they get more lumber than the scale predicted.
• Large Logs: On very large logs, the scale can become more accurate or occasionally overestimate volume, depending on the taper and the saw kerf (the width of the saw blade).

Practical Examples

Log Diameter	Log Length	Board Feet (Doyle)
12 inches	16 feet	64 bf
18 inches	12 feet	147 bf
24 inches	16 feet	400 bf

Frequently Asked Questions

1. Why do I subtract 4 inches from the diameter?

The 4-inch deduction is intended to account for the "slab" (the rounded exterior of the log) and the "kerf" (the sawdust created by the saw blade). It assumes a standard waste factor for turning a round log into square lumber.

2. Is Doyle better than the International 1/4″ scale?

The International 1/4″ scale is technically more accurate for modern sawmills because it accounts for log taper. However, Doyle is still the industry standard for buying standing timber or logs at the gate in many regions because of its historical consistency.

3. Does this include the bark?

No. You must always measure the diameter inside the bark. Measuring the outside of the bark will lead to a significant overestimation of the actual lumber yield.