Board Feet in a Log Calculator
Estimate the lumber yield from a log using three standard log scaling rules.
International 1/4″ Rule
Doyle Rule
Scribner Rule
Comparison of Log Scale Rules
Example Board Foot Yields (International 1/4″ Rule)
| Diameter (in) | 8 ft Length (BF) | 12 ft Length (BF) | 16 ft Length (BF) |
|---|
What is a Board Foot?
A board foot (BF) is the standard unit of volume for lumber in the United States and Canada. It represents a piece of wood that is one foot long, one foot wide, and one inch thick. The total volume in board feet is calculated before the lumber is planed and finished, so it refers to the rough-sawn volume. When you use a board feet in a log calculator, you are not calculating the log’s total volume, but rather estimating the amount of usable lumber that can be milled from it.
Log scaling rules, like Doyle, Scribner, and International, are different formulas created to provide this estimate. They attempt to account for the material that will be lost to sawdust (kerf), the rounded sides of the log (slabs), and in some cases, the natural taper of the log. Because each rule makes different assumptions, they produce different results, which is why foresters and sawmills must agree on which rule to use when buying or selling logs.
Board Feet Formulas and Explanation
There is no single formula for a board feet in a log calculator; instead, there are several competing “log rules.” This calculator provides results for the three most common ones.
- Doyle Log Rule: This rule is one of the oldest and simplest. It heavily penalizes small-diameter logs.
BF = ((D - 4) / 4)^2 * L - Scribner Log Rule: This rule was created from diagrams of how many 1-inch boards could be fit into circles of different diameters. It is more accurate than Doyle on smaller logs but does not account for log taper. A common formula approximation is:
BF = (0.79 * D^2 - 2*D - 4) * L / 16 - International 1/4-Inch Rule: This is the most complex but also the most accurate of the three, as it is the only one that accounts for both saw kerf and a standard log taper (1/2 inch of diameter for every 4 feet of length). It calculates volume in 4-foot segments.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| BF | Board Feet | (Unitless Volume Measure) | 5 – 2000+ |
| D | Log Diameter | Inches (inside bark, small end) | 8 – 48 |
| L | Log Length | Feet | 8 – 40 |
Practical Examples
Example 1: A Standard Hardwood Log
Let’s say you have a red oak log that you plan to use for furniture. You measure it and find:
- Inputs:
- Log Diameter (D): 18 inches
- Log Length (L): 12 feet
- Results:
- International 1/4″ Rule: ~140 BF
- Doyle Rule: 110 BF
- Scribner Rule: 125 BF
As you can see, the International rule predicts the highest yield, while the Doyle rule predicts the lowest. This is typical for logs of this size. For more information, you might want to look into a Lumber Weight Calculator to estimate the weight of your milled boards.
Example 2: A Large Softwood Log
Now consider a large pine log destined for construction lumber.
- Inputs:
- Log Diameter (D): 30 inches
- Log Length (L): 20 feet
- Results:
- International 1/4″ Rule: ~545 BF
- Doyle Rule: 531 BF
- Scribner Rule: 520 BF
On larger logs, the Doyle rule “catches up” and can sometimes overestimate the yield compared to the other rules. The Scribner rule often gives the most conservative estimate for large logs. Understanding log scaling is the first step in a Woodworking Project Planner.
How to Use This Board Feet in a Log Calculator
Using this calculator is a straightforward process:
- Measure Diameter: The most critical measurement is the diameter of the log at its smallest end. Be sure to measure *inside* the bark. If the log isn’t perfectly round, take two measurements at 90 degrees to each other and average them. Enter this value in the “Log Diameter” field in inches.
- Measure Length: Measure the length of the log from one end to the other. Enter this value in the “Log Length” field in feet.
- Review Results: The calculator automatically updates the board foot estimates for the International, Doyle, and Scribner rules. The International 1/4″ rule is highlighted as it’s generally the most accurate predictor of actual lumber yield.
- Interpret the Chart and Table: Use the dynamic bar chart to quickly visualize the difference between the scales. The table below the chart provides pre-calculated examples for common log sizes.
Key Factors That Affect Board Foot Yield
The estimate from any board feet in a log calculator is just that—an estimate. The actual amount of lumber you get from a log is affected by several real-world factors:
- Log Taper: Logs are wider at the base than at the top. Only the International 1/4″ Rule explicitly accounts for this. High taper reduces yield.
- Saw Kerf: The thickness of the saw blade determines how much wood is turned into sawdust. A thin-kerf bandsaw will yield more lumber than a thick-kerf circular saw.
- Defects: Knots, rot, cracks, and sweep (curvature) in the log will all reduce the amount of usable, high-grade lumber. A scaler will make deductions for these defects.
- Sawyer’s Skill: An experienced sawyer can read a log and make cuts to maximize the yield of high-value boards, increasing the total board footage.
- The Log Rule Itself: As shown by the calculator, the choice of log rule is one of the biggest factors. The Doyle rule, for instance, was designed to favor the sawmill buyer by under-scaling small logs.
- Shrinkage: Wood shrinks as it dries. While log scales measure the “green” volume, the final volume of dried lumber will be less. To plan accurately, consider the Wood Shrinkage Calculator.
Frequently Asked Questions
1. Why are there different log scaling rules?
Different rules were developed in different regions and time periods for different purposes. Some, like Doyle, were simple and favored buyers. Others, like International, were scientifically designed to be more accurate. The persistence of multiple rules is due to historical and regional traditions in the timber industry.
2. Which log scale is the most accurate?
The International 1/4-Inch Rule is widely regarded as the most accurate because it’s the only common rule that accounts for both log taper and a fixed saw kerf allowance.
3. Does this calculator account for bark?
No. You should always measure the diameter *inside* the bark for an accurate scaling measurement.
4. What is “overrun”?
Overrun is the difference between the scaled board foot estimate of a log and the actual amount of lumber sawn from it. With modern, thin-kerf sawmills, it’s common to have a positive overrun, especially when using the Doyle or Scribner scales.
5. Can I use this for firewood?
No. This calculator estimates usable lumber volume. Firewood is typically measured in cords, which is a measure of stacked volume (128 cubic feet). See our Cord of Wood Calculator for that purpose.
6. How do I measure an out-of-round log?
Take the widest diameter and the narrowest diameter at the small end of the log (inside the bark) and average them together.
7. What is the difference between board feet and linear feet?
A board foot is a measure of volume (Length x Width x Thickness), while a linear foot is simply a measure of length (12 inches). Lumber is sold by the board foot, while trim or molding is often sold by the linear foot.
8. Why does the Doyle rule give such low values for small logs?
The formula subtracts 4 inches from the diameter to account for slabs. This deduction is disproportionately large for small logs (e.g., a 10-inch log is treated as a 6-inch log), resulting in a significant underestimate of yield.