Doyle Log Rule Calculator

The Doyle Log Rule Calculator calculates timber yield in board feet from log diameter and length using the Doyle rule.

About the Doyle Log Rule Calculator

The Doyle rule is a traditional lumber scaling method used to estimate log volume in board feet. A board foot is a unit of lumber volume equal to 144 cubic inches, or a board 12 inches by 12 inches by 1 inch thick. The rule uses the small-end diameter of a log and the log’s length to estimate yield. It assumes a taper and cutting loss pattern typical of older sawmilling practice.

This calculator applies the standard Doyle formula. It accepts diameter inside bark at the small end in inches and the length in feet. The output is board feet for a single log and can be summarized in thousand board feet (MBF) for multiple logs. You can adjust inputs easily to reflect your log’s dimensions and to compare different estimates.

The Doyle rule tends to be conservative for small logs and closer to actual sawn volume for medium and larger logs. Because of its simplicity, it remains common in forestry, timber sales, and construction materials planning. Use it when a quick, consistent estimate is needed and the Doyle standard is expected by buyers or contracts.

How to Use Doyle Log Rule (Step by Step)

Before you begin, measure the log’s small-end diameter inside bark. “Small-end diameter” means the diameter of the narrow end of the log; “inside bark” means bark thickness is excluded. Measure log length along the centerline from end to end. Have a tape, calipers, or a diameter ruler ready.

• Clean a small, flat spot at the small end and measure diameter inside bark in inches.
• Measure the log length in feet, typically in 2-foot increments if following common scaling practice.
• Enter diameter and length in the Calculator inputs.
• Choose the number of logs if you want a subtotal in MBF (thousand board feet).
• Review the result and note any warnings for very small diameters or atypical lengths.

Repeat for each log you want to assess. If you are comparing different bucking lengths, run the calculation for each option and pick the length that best fits your target volume and product mix.

Formulas for Doyle Log Rule

The Doyle rule is expressed in a compact equation that uses diameter in inches and length in feet. The formula subtracts a fixed allowance to cover slab and kerf. Kerf is the saw blade thickness removed as sawdust during cutting. The result is reported in board feet.

• Primary formula: Volume (board feet) = ((D − 4)² × L) ÷ 16
• D = small-end diameter inside bark in inches
• L = log length in feet
• Output units: board feet (bf); 1 MBF = 1,000 bf

The term (D − 4)² reduces small log volumes to account for slabs and disproportionate losses. For D ≤ 4 inches, the formula yields zero or negative values; practical scaling sets the result to zero. Some regional tables round volumes by length class; the calculator computes the continuous form and rounds to the nearest board foot.

Inputs, Assumptions & Parameters

Enter measurements that match the Doyle assumptions, and note where your situation differs. Accurate inputs lead to better estimates. Below are the main inputs and their meaning.

• Small-end diameter inside bark (in): Measured at the smaller end of the log. Remove bark thickness from your measurement.
• Log length (ft): Measured along the centerline. Many mills prefer 8, 10, 12, 14, or 16 feet, plus trim.
• Number of logs: Used for totaling board feet and reporting in MBF.
• Measurement units: Use inches for diameter and feet for length. Convert metric dimensions before entry if needed.
• Rounding: Choose whether to round to whole board feet or keep decimals for analysis.

Edge cases matter. For D ≤ 4 inches, Doyle volume is zero. Very short logs below 8 feet may not be accepted by many mills. For long logs, confirm mill limits and required trim. If your measurements are metric, convert units before calculating to avoid scaling errors.

Step-by-Step: Use the Doyle Log Rule Calculator

Here’s a concise overview before we dive into the key points:

1. Measure the small-end diameter inside bark in inches and record it.
2. Measure the log length in feet along the centerline and record it.
3. Open the Calculator and enter diameter and length in their fields.
4. Set the number of logs, if totaling multiple pieces.
5. Click Calculate to compute board feet per log and totals.
6. Review the result and any notes about small diameters or unusual lengths.

These points provide quick orientation—use them alongside the full explanations in this page.

Worked Examples

A logger has a hardwood log with a small-end diameter of 16 inches and a length of 12 feet. Using Doyle: Volume = ((16 − 4)² × 12) ÷ 16 = (12² × 12) ÷ 16 = (144 × 12) ÷ 16 = 1728 ÷ 16 = 108 board feet. If there are 10 similar logs, total is 1,080 board feet, or 1.08 MBF. This is a practical estimate for pricing and hauling decisions. What this means

A landowner is bucking a tree and must choose between one 16-foot log or two 8-foot logs from the same stem. First option: D = 14 inches, L = 16 feet; Volume = ((14 − 4)² × 16) ÷ 16 = (10² × 16) ÷ 16 = 100 board feet. Second option: two 8-foot logs at D = 14 and D = 13 inches due to taper. Volumes: ((10² × 8) ÷ 16) = 50 bf and ((9² × 8) ÷ 16) = 40.5 bf; total ≈ 90.5 bf. The single 16-foot log yields about 9.5 bf more under Doyle. What this means

Accuracy & Limitations

Doyle is simple and widely used, but it is not perfect. It tends to undervalue small logs and may better reflect volume for medium to larger logs. Mill recovery also depends on species, sweep, crook, and sawing pattern, which the rule does not model.

• Small logs: Doyle can underestimate volume compared to actual sawn output.
• Large logs: Estimates improve as diameter increases, but defects still affect recovery.
• Defects: Sweep, rot, and knots are not in the formula; deduct separately per local rules.
• Dimensions: Length classes and required trim vary by mill and region.
• Units: Mixing metric and imperial units can produce large errors if not converted correctly.

Use Doyle when contracts specify it or when comparing options consistently. For a more balanced view across sizes, compare with other rules like Scribner and International 1/4-inch, or confirm with actual mill tallies.

Units & Conversions

Accurate unit handling keeps your estimate reliable. The Doyle formula expects diameter in inches and length in feet, with output in board feet. If you measure with metric tools, convert dimensions before calculating and convert results to cubic meters if needed.

To use the table, multiply your measurement by the conversion factor. For example, 400 board feet is 400 ÷ 12 = 33.33 cubic feet, or about 0.944 m³. Keep conversions consistent across all logs to maintain a fair comparison.

Troubleshooting

If your result looks wrong, first check your inputs and units. The most common problem is entering outside-bark diameter or metric values without converting. Another frequent issue is measuring length along the bark rather than the log’s centerline.

• Volume is zero: Your diameter may be 4 inches or less, or you entered centimeters instead of inches.
• Numbers seem too high: Confirm you used small-end diameter and not the large end.
• Totals do not match: Check the number of logs and rounding settings.

If values still look off, remeasure the log end, subtract bark, and retry. When in doubt, compare your reading with a printed Doyle rule table for the same dimensions to confirm the calculation.

FAQ about Doyle Log Rule Calculator

What is a board foot, and why does Doyle use it?

A board foot is 144 cubic inches of lumber volume. It reflects sawn lumber output and is the standard unit for buying and selling logs and lumber in many regions.

Should I measure diameter inside bark or outside bark?

Measure diameter inside bark at the small end. Bark thickness varies by species and season; including bark would overstate volume.

How does Doyle compare to Scribner or International 1/4-inch?

Doyle is generally conservative on small logs, while Scribner and International 1/4-inch often provide higher estimates there. Choice depends on local practice and contract terms.

Can I use metric measurements with this method?

Yes. Convert diameter to inches and length to feet before applying the formula, then convert the board-foot result to cubic meters if needed.

Key Terms in Doyle Log Rule

Board Foot (bf)

A unit of lumber volume equal to 144 cubic inches, typically a board 12 inches by 12 inches by 1 inch thick. It is the output unit of the Doyle formula.

Small-End Diameter

The diameter of the narrower end of a log. This measurement drives the Doyle estimate because it represents the limiting cross-section.

Inside Bark (IB)

A measurement taken after excluding bark thickness. Using inside bark yields a closer link to possible lumber volume.

Kerf

The thickness of material removed by the saw blade during cutting. The Doyle rule’s “minus four inches” term partly reflects kerf and slab losses.

Taper

The gradual reduction in log diameter from the butt to the top. Taper reduces recoverable lumber and is indirectly addressed by using the small-end diameter.

MBF

An abbreviation for thousand board feet. It is a convenient way to total multiple logs or a truckload.

Scaling

The process of measuring logs and applying a rule to estimate the sawn lumber volume. Scaling can use Doyle or other rules depending on region and contract.

Log Length

The end-to-end measurement along the log centerline, reported in feet for Doyle calculations. Mills often prefer even lengths with trim.

Sources & Further Reading

Here’s a concise overview before we dive into the key points:

• Penn State Extension: Log Scaling Using the Doyle Rule
• USDA Forest Service: Log Rules for Estimating Board-Foot Volume
• Ohio State University Extension: Understanding Log Rules
• USDA Agriculture Handbook: Cubic and Board-Foot Volume Tables
• Michigan State University Extension: Log Scaling and Log Rules

These points provide quick orientation—use them alongside the full explanations in this page.