Log Calculator
Understanding Your Results
Small Logs (6-12 inches)
Small diameter logs typically yield less lumber and may have lower board foot values. Doyle rule significantly underestimates these logs, so Scribner or International rules are recommended. These logs are often used for pallets, crating, or small dimensional lumber. Expect higher waste percentages due to the proportion of bark and sapwood.
Medium Logs (12-24 inches)
Medium logs are the most common commercial size and provide good yields across all three rules. This range is ideal for dimensional lumber, flooring, and general construction materials. All three scaling rules give reasonable estimates, with Scribner being the industry standard for pricing. These logs offer the best balance of value and processing efficiency.
Large Logs (24+ inches)
Large diameter logs are premium timber with high board foot values. They're ideal for wide boards, veneer, and specialty products. International rule is most accurate for these valuable logs. Consider using International rule for pricing negotiations. These logs can produce clear, wide boards that command premium prices in the market.
What is Log Board Foot?
A board foot is a standard unit of measurement for lumber volume. When measuring logs, three industry-standard scaling rules are used: Doyle, Scribner, and International. Each rule uses different formulas to estimate the usable lumber that can be milled from a log. The Doyle rule is conservative and best for smaller logs, Scribner is the most widely used standard in the US lumber industry, and the International rule provides the most accurate mathematical model. Understanding these differences helps you make informed decisions when buying or selling logs.
Calculation Examples
Small Pine Log
A small pine log measuring 10 inches diameter and 8 feet long using Scribner rule.
Calculation Steps
- Input: 10" diameter, 8' length
- Formula: (0.79 × 10² - 2 × 10 - 4) × (8/16)
- Calculation: (0.79 × 100 - 20 - 4) × 0.5 = 31 BF
Medium Oak Log - Three Rules Comparison
An 18-inch diameter oak log, 12 feet long, compared across all three rules.
Calculation Steps
- Doyle: ((18-4)² × 12) / 16 = 147 BF
- Scribner: (0.79 × 18² - 2 × 18 - 4) × (12/16) = 180 BF
- International: (0.22 × 18² - 0.71 × 18) × (12/16) = 62.6 BF
Large Hardwood Log
A premium 30-inch diameter hardwood log, 16 feet long, using International rule for precision.
Calculation Steps
- Input: 30" diameter, 16' length, 0.5 taper
- Formula: (0.22 × 30² - 0.71 × 30) × (16/16)
- Calculation: (0.22 × 900 - 21.3) × 1 = 177 BF
How to Calculate
Measure the Log
Measure the diameter at the small end of the log (inside bark) and the length. Use a diameter tape or caliper for accuracy. Round down to the nearest inch for diameter.
Choose Your Rule
Select Doyle for conservative estimates, Scribner for standard industry calculations, or International for precise mathematical results. You can also compare all three rules at once.
Enter Values
Input the diameter (6-60 inches) and length (4-40 feet) into the calculator. For International rule, you can optionally adjust the taper value (default 0.5 inch/foot).
Review Results
View the board feet calculation for your selected rule. Use the comparison feature to see how all three rules differ. Copy results or adjust parameters as needed.
Why Three Different Rules?
Doyle Rule (1825)
The oldest scaling rule, developed by Edward Doyle. It's conservative and deducts 4 inches for saw kerf, making it best suited for logs 12 inches and larger. While it underestimates yield for small logs, it's still used in some regions for its simplicity.
Scribner Rule (1846)
Developed by J.M. Scribner, this is the most widely used scaling rule in the United States. Based on actual log diagrams, it provides realistic estimates for commercial timber. It's the industry standard for most timber sales and is recognized by the USDA Forest Service.
International Rule (1917)
The most mathematically precise rule, developed by Judson F. Clark. It accounts for 1/4-inch saw kerf and taper, providing the most accurate estimate of recoverable lumber. It's preferred for high-value logs and international trade where precision matters.
Input Parameters Explained
Diameter (Small End)
The diameter measured at the small end of the log, inside the bark. This is the standard measurement point for all scaling rules. Measure in inches, accurate to 0.1 inch. Valid range is 6-60 inches.
Length
The length of the log in feet. Standard log lengths are 8, 10, 12, and 16 feet, but any length from 4-40 feet is supported. Measure from end to end, excluding any defects or rot.
Scaling Rule
Choose between Doyle (conservative), Scribner (industry standard), or International (most accurate). Each rule uses a different formula and will give different results for the same log dimensions.
Taper (Optional)
Only used with International rule. Represents how much the log diameter decreases per foot of length. Default is 0.5 inch/foot. Higher taper means more diameter reduction along the log length.
Scaling Rules Formulas
All formulas assume standard sawing practices and average log quality. Actual yield may vary based on sawmill efficiency, log defects, and market conditions.
Doyle Rule
Where D is diameter in inches and L is length in feet. Subtracts 4 inches for saw kerf and slabbing. Best for logs 12 inches and larger.
Board Feet = ((D - 4)² × L) / 16
Example: 16" × 12' log: ((16-4)² × 12) / 16 = 108 BF
Scribner Rule
Approximation formula based on Scribner log tables. Provides realistic estimates for commercial timber. Industry standard in the United States.
Board Feet = (0.79 × D² - 2 × D - 4) × (L / 16)
Example: 16" × 12' log: (0.79 × 16² - 2 × 16 - 4) × (12/16) = 143 BF
International Rule
Mathematical formula accounting for 1/4-inch saw kerf. Most accurate for estimating recoverable lumber. Preferred for high-value logs.
Board Feet = (0.22 × D² - 0.71 × D) × (L / 16)
Example: 16" × 12' log: (0.22 × 16² - 0.71 × 16) × (12/16) = 47.9 BF
Frequently Asked Questions
The International rule is mathematically the most accurate, as it accounts for saw kerf and taper with precision. However, 'accuracy' depends on your purpose. Scribner is the industry standard for commercial transactions in the US, while Doyle is conservative and often used for smaller operations. For high-value logs or international trade, International rule is preferred.
Each rule was developed at different times with different assumptions about sawing practices and waste. Doyle (1825) is very conservative and deducts 4 inches for slabbing. Scribner (1846) is based on actual log diagrams. International (1917) uses mathematical formulas with 1/4-inch kerf. These different approaches lead to variations of 10-30% between rules for the same log.
Always measure the diameter at the small end of the log, inside the bark. This is the standard measurement point for all scaling rules. Use a diameter tape or caliper for accuracy, and round down to the nearest inch. Measuring at the small end ensures a conservative estimate of usable lumber.
Yes, but logs shorter than 8 feet may have reduced yield efficiency due to end trimming and setup waste. The calculator accepts lengths from 4-40 feet. For logs under 8 feet, expect actual mill yield to be lower than calculated board feet due to proportionally higher waste.
Taper (only used in International rule) represents how much the log diameter decreases per foot of length. Default is 0.5 inch/foot. Higher taper means more diameter reduction and slightly lower board feet. Most logs have 0.3-0.7 inch/foot taper. Taper adjustment provides more accurate estimates for logs with significant diameter change.
A board foot is a unit of measurement for lumber volume, equal to a board 1 foot long, 1 foot wide, and 1 inch thick (144 cubic inches). It's the standard unit for pricing and selling lumber in North America. When measuring logs, board feet represents the estimated amount of usable lumber that can be milled from the log.