Doyle Board Foot Calculator: Log Scale Explained

The Doyle board foot calculator estimates the number of board feet you can saw from a log using the Doyle Log Scale, the most common rule in the eastern United States. You enter the small-end diameter (inside bark) in inches and the log length in feet; the calculator returns the estimated board foot yield. This is a quick, practical tool for timber valuation, firewood planning, or comparing logs before you buy.

Formula

The Doyle rule is a simple, century-old formula:

Board Feet = ((D – 4) / 4)² × L

• D = small-end diameter inside bark, in inches (the diameter of the log’s narrow end, excluding bark)
• L = log length, in feet
• Board feet = volume in nominal board feet (1 board foot = 1 ft × 1 ft × 1 in, or 144 cubic inches)

The formula subtracts 4 inches from the diameter to account for saw kerf (the width of the saw blade cut) and slab waste, then squares the remaining quarter-inches of diameter and multiplies by length. It intentionally underestimates small logs and overestimates large ones compared to actual sawmill output, but its simplicity and long history keep it the default in many regions.

Worked Example

Using the calculator defaults (small-end diameter = 16 inches, length = 10 feet):

1. Subtract 4 from the diameter: 16 – 4 = 12
2. Divide by 4: 12 / 4 = 3
3. Square the result: 3² = 9
4. Multiply by length: 9 × 10 = 90 board feet

The calculator shows 90 board feet for a 16-inch, 10-foot log. The MBF output is 0.090 thousand board feet (90 / 1000).

How the Doyle Scale Compares to Other Log Rules

The Doyle rule is not the only way to estimate log volume. Two other common rules are the Scribner and International 1/4-inch rules. Each gives different numbers for the same log.

• Doyle: Underestimates logs under about 28 inches in diameter; overestimates very large logs. Best for quick estimates, especially for small to medium hardwood logs.
• Scribner: Uses a diagram of log cross-sections showing where boards can be cut. More accurate for medium logs (10–30 inches), and generally gives higher values than Doyle for small logs.
• International 1/4-inch: The most accurate rule, accounting for saw kerf and shrinkage. It gives the closest estimate to actual mill output but is more complex to calculate.

For a 16-inch, 10-foot log, Doyle gives 90 board feet; Scribner gives about 110; International gives about 115. The difference matters when you are pricing timber or estimating a truckload’s value.

How to Measure a Log Correctly

The Doyle formula is only as good as your measurements. Follow these steps to get accurate inputs:

1. Find the small end: The diameter is always measured at the narrow end of the log, not the butt end.
2. Measure inside bark: Peel back or ignore the bark thickness. Bark can add 1–2 inches to the diameter, which inflates the estimate.
3. Measure diameter in inches: Use a diameter tape or a regular tape measure and divide the circumference by π (3.1416). Round to the nearest inch.
4. Measure length in feet: Logs are typically cut in 2-foot increments (8, 10, 12, 14, 16 ft). Use the actual length, not the nominal length.
5. If the log is tapered: The Doyle rule assumes a uniform cylinder, so a heavily tapered log will yield less than the formula suggests.

For multiple logs, add the board feet of each log together. The calculator handles one log at a time, so you would run it per log.

Common Mistakes and Misconceptions

• Using the large end diameter: The formula expects the small end. Using the butt end overestimates volume.
• Including bark in the diameter: Bark is not lumber. Always measure inside bark.
• Mixing units: Diameter in inches, length in feet. If you measure length in inches, the result will be wildly off.
• Thinking the result is exact: The Doyle rule is an estimate. Actual sawmill yield depends on log shape, defects, saw blade thickness, and the mill’s efficiency.
• Applying Doyle to all regions: The western US often uses Scribner; the International rule is common for export logs. Know which rule your buyer or seller uses.

Why the Doyle Rule Underestimates Small Logs

For a 10-inch, 8-foot log, Doyle gives only 18 board feet, while the actual mill might get 30–40. The reason is the fixed 4-inch deduction. A 10-inch log loses 4 inches to saw kerf and slabs, which is a huge proportion of its volume. A 30-inch log loses the same 4 inches, which is a much smaller fraction. This makes Doyle conservative for small logs—useful if you want a safe estimate, but misleading if you are comparing log prices and assume all rules are equal.

Practical Uses and Limits

The Doyle board foot calculator is most useful for:

• Timber buying/selling: Many hardwood buyers in the eastern US quote prices per thousand board feet (MBF) using Doyle.
• Estimating lumber yield: If you are sawing your own logs, it gives a rough idea of how many boards you will get.
• Comparing logs: When deciding which trees to cut, the formula helps rank logs by volume.

Limits: The rule does not account for defects (knots, rot, crook), taper, or sawmill efficiency. It also assumes the log is perfectly round and straight, which is rarely true. For high-value timber, a professional cruiser or a mill’s actual tally is more reliable.

Frequently Asked Questions

What is a board foot?

A board foot is a unit of lumber volume equal to 1 foot wide × 1 foot long × 1 inch thick, or 144 cubic inches. It is the standard measure for rough lumber in the US and Canada.

Why is it called the Doyle rule?

The rule was developed by a man named Edward Doyle in the mid-1800s, likely in the eastern United States. It became popular because it was easy to remember and apply, even though it is less accurate than later rules.

How do I convert Doyle board feet to cubic meters?

One board foot equals 0.0023597 cubic meters (1 board foot = 1/424 m³, the international standard for roundwood is often 1 m³ = 424 board feet using the Doyle rule). Multiply the board feet by 0.00236 to get cubic meters.

Does the calculator work for metric measurements?

No, the Doyle formula is defined in inches and feet. If you have metric measurements, convert diameter to inches (1 cm = 0.3937 in) and length to feet (1 m = 3.2808 ft) before using the calculator.

What is MBF and why do I see it in timber prices?

MBF stands for “thousand board feet� (or M board feet, where M is the Roman numeral for 1000). Timber prices are often quoted per MBF, so a price of $300/MBF means $300 per 1,000 board feet. The calculator’s MBF output helps you compare prices.

Can I use this for firewood?

No, firewood is measured in cords, not board feet. A cord is 128 cubic feet of stacked wood (4 ft × 4 ft × 8 ft). The Doyle rule is for sawlogs intended for lumber, not firewood.

Related

• Board and Batten Calculator: Siding & Spacing
• Board Foot to m3 Calculator: Quick Conversion
• Board Foot to Piece Calculator: Lumber Math

in d | Small-end diameter (in) | in | 16 | 0
in l | Log length (ft) | ft | 10 | 0
out bf | Doyle board feet | bd ft | ((d-4)/4)^2 * l | 0
out mbf | Thousand board feet (MBF) | MBF | (((d-4)/4)^2 * l) / 1000 | 3