What Is the Doyle Log Scale? (Board Foot Chart)
The Doyle log scale is a rule for estimating the board-foot volume of a log from its small-end diameter and merchantable length. Its formula is ((D-4)^2 \times L \div 16), with diameter in inches and length in feet. Use the chart below as a quick reference, but first agree on bark, length, deductions, and rounding rules.
A log scale can look like a lumber measurement, but it is an estimate of log volume, not a count of boards the mill will produce. That difference matters when you are buying, selling, or checking a tally. The useful part is that the Doyle rule turns two measurements into a consistent estimate. The important part is using the same measuring rules as the other party.
Equipment Setup and Scaling-Rule Safety Prep
Before measuring, agree that the Doyle rule applies and confirm how each log will be measured. “Small-end diameter” and “merchantable length” sound simple, but bark, trim, and rounding can change the tally. Write down the agreed method before you begin so both sides use the same basis.
The Doyle scale is a log rule, not an equipment specification or a direct measurement of finished lumber. It estimates board feet from a log’s small end and usable length. A tape or scale stick can help you take measurements, but the buyer’s or seller’s written scaling terms determine how those measurements are used.
Before scaling, confirm these points:
- Scaling rule: Both parties must agree to use Doyle. Other log rules use different formulas or measurement methods, so their results are not interchangeable.
- Bark convention: Confirm whether diameter is measured inside bark or outside bark. Doyle tables generally use small-end diameter, commonly measured inside bark, but the agreed local rule may specify otherwise.
- Length and trim: Use the merchantable log length, not the tree’s total height. Confirm accepted log-length increments and how trim allowance is handled.
- Deductions and rounding: Ask how defects are treated and when values are rounded. Do not assume that every buyer or jurisdiction uses the same procedure.
If the agreed rule calls for inside-bark diameter, measuring outside bark can produce a larger estimate. That difference can affect a payment or inventory tally. I would settle the bark convention first, then measure every log the same way.
Field Log Measurement and Doyle Board-Foot Calculation
For each log, record its small-end diameter in inches and its merchantable length in feet. Apply the Doyle formula, or find the matching size in the chart. The result is nominal board feet: a standard volume estimate under this rule, not a promise of how much usable lumber a mill will recover.
The Doyle formula is:
Board feet = ((D-4)^2 \times L \div 16)
- D is the small-end diameter in inches, measured by the agreed convention.
- L is the merchantable log length in feet.
- The answer is a nominal board-foot estimate under the Doyle rule.
The formula’s fixed subtraction of 4 inches is part of the rule. It is not a measurement of your saw’s kerf or a separate trim allowance. Do not change the formula to account for those factors unless the agreed scaling method specifically requires a separate adjustment.
Doyle board-foot chart
The values below come from the Doyle formula. Diameters are in inches, lengths are in feet, and fractional results are rounded to the nearest board foot for this chart.
| Small-end diameter | 8 ft | 10 ft | 12 ft | 14 ft | 16 ft |
|---|---|---|---|---|---|
| 8 in | 8 | 10 | 12 | 14 | 16 |
| 10 in | 18 | 23 | 27 | 32 | 36 |
| 12 in | 32 | 40 | 48 | 56 | 64 |
| 14 in | 50 | 63 | 75 | 88 | 100 |
| 16 in | 72 | 90 | 108 | 126 | 144 |
| 18 in | 98 | 123 | 147 | 172 | 196 |
| 20 in | 128 | 160 | 192 | 224 | 256 |
| 24 in | 200 | 250 | 300 | 350 | 400 |
To calculate a 14-inch small-end diameter log that is 12 feet long:
- Subtract 4 from the diameter: (14-4=10).
- Square the result: (10 \times 10=100).
- Multiply by length: (100 \times 12=1{,}200).
- Divide by 16: (1{,}200 \div 16=75) board feet.
For a 10-inch diameter, 10-foot log, the result is ( (10-4)^2 \times 10 \div 16 = 22.5) board feet. The chart shows 23 because it rounds that value to the nearest whole board foot. Keep unrounded values until the agreed tally procedure calls for rounding.
Worked scaling scenarios
These examples show how to apply the rule. They are calculation examples, not reports of particular timber sales or guaranteed mill recovery.
| Scenario | Measurement used | Doyle estimate |
|---|---|---|
| Shorter log | 12 in diameter, 8 ft long | 32 board feet |
| Longer log, same diameter | 12 in diameter, 16 ft long | 64 board feet |
| Larger small end, same length | 16 in diameter, 12 ft long | 108 board feet |
| Chart value with a fraction | 10 in diameter, 10 ft long | 22.5, or 23 on the rounded chart |
Building on the first example, doubling length doubles the formula result when diameter stays the same. A larger diameter also raises the estimate, because the formula squares the diameter after subtracting 4. Keep those relationships in mind when checking whether a chart entry seems plausible.
Scale Verification, Deductions, and Recordkeeping
A reliable Doyle tally depends on consistent measurements and clear notes. Measure each log separately, apply the agreed rule, and document any deductions or rounding. The total is an estimate of log volume under that procedure; it does not guarantee the amount of finished lumber after sawing.
Use this sequence for a tally:
- Confirm the rules. Record the Doyle rule, bark convention, measurement method, length increments, trim treatment, defect deductions, and rounding method.
- Measure each log. Measure the small end at the location specified by the agreed method. Record the merchantable length rather than the tree’s full height.
- Calculate the estimate. Use the formula or chart. Keep the exact or unrounded result until the agreed rounding step.
- Check the entries. Compare chart lookups with formula calculations when a value seems off. Confirm the diameter and length units before adding a log to the total.
- Report the tally. Keep each log’s measurements, any deductions, its calculated value, and the final total together.
For example, a tally might list a log as “14-inch small end, 12 feet, 75 Doyle board feet,” followed by the agreed bark convention and any applicable deduction. This makes it easier for another person to check the math without guessing how the diameter was taken.
A chart is a quick lookup tool, not a replacement for the agreed method. It includes only certain diameters and lengths, and its fractional values are rounded. If a log does not match a chart row or column, calculate it from the formula and follow the contract’s rounding instructions.
Storage, Seasonal Conditions, and Scale Documentation
The Doyle formula does not change with the season, but a repeat measurement may be harder to compare if the log’s condition or measuring method has changed. Record when and how the log was scaled, along with the bark convention and dimensions. Keep those details with the tally so later checks use the same basis.
A simple record can include:
- Date of measurement
- Log identification or tally number
- Small-end diameter and how bark was handled
- Merchantable length and trim convention
- Doyle estimate before rounding
- Any agreed deductions and the final rounded value
Avoid mixing measurements taken under different conventions in one tally. For example, do not combine inside-bark diameters for some logs with outside-bark diameters for others unless the agreed rule explicitly directs that method. If logs are measured again later, note the date and method rather than silently replacing the original figures.
The chart and formula estimate log volume; they do not predict finished-lumber recovery. Taper, defects, log shape, kerf, and sawing practice affect what can be recovered. Treat a Doyle result as a scaling figure for the stated rule, not as guaranteed board output.
FAQ
What does the Doyle log scale measure?
It estimates board-foot volume in a log using the small-end diameter and merchantable length. It does not measure finished boards or guarantee the amount of lumber a mill will produce.
What is the Doyle formula?
The formula is ((D-4)^2 \times L \div 16). Use diameter (D) in inches and merchantable length (L) in feet, following the agreed measurement and rounding rules.
Which end of the log do I measure?
The formula uses the small-end diameter. Confirm the exact measuring method and bark convention with the buyer, seller, contract, or applicable local scaling rule.
Is Doyle diameter measured inside or outside bark?
Doyle tables commonly use small-end diameter inside bark, but the applicable rule or agreement may specify otherwise. Confirm this before measuring; using outside bark when inside bark is required can overstate the estimate.
Does the Doyle scale tell me how many boards I will get?
No. It provides a nominal log-volume estimate. Taper, defects, kerf, log shape, and sawing practice affect actual lumber recovery.
How do I use the chart for a length it does not show?
Apply the formula using the log’s measured diameter and merchantable length. Keep fractional results until the agreed scaling procedure says how to round.
Should I round each log or the final total?
Follow the stated scaling rule or contract. The chart rounds fractional results to the nearest board foot, but a tally may require a different rounding procedure.
Can I compare a Doyle total directly with another log rule?
Not reliably without identifying the other rule and its measurement conventions. Different scaling rules may use different formulas and methods, so their estimates are not interchangeable.
What should I confirm before a Doyle tally?
Agree on the rule, bark convention, diameter method, length increments, trim, defect deductions, and rounding. Record those choices with the log measurements and total.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
