Board Foot Calculator: How to Calculate Board Feet in a Log

Estimate the usable lumber from a log with our precise calculator.

Visual Comparison of Log Rules

Chart comparing the estimated board feet for the given log dimensions across the three common scaling rules.

What Is a Board Foot?

A board foot (BF or BDFT) is the standard unit of volume for lumber in the United States and Canada. It represents the volume of a one-inch thick board that is one foot wide and one foot long. In essence, 1 Board Foot = 144 cubic inches. When you need to know how to calculate board feet in a log, you are estimating the total volume of usable lumber that can be milled from that log. This calculation is not an exact science, as the actual yield depends on many factors, but log scaling rules provide a standardized estimate.

Foresters, sawmill operators, and woodworkers use this measurement to value logs and timber stands. There are several different methods, or “log rules,” to make this estimation, with the most common being the Doyle, Scribner, and International 1/4-Inch rules. Each rule has its own mathematical formula and accounts for waste like saw kerf (the width of the saw cut) and slabbing differently.

Log Scaling Formulas and Explanations

Log scaling rules are formulas used to estimate the number of board feet of lumber that can be sawn from a log. The three most prevalent rules in North America each have a unique approach.

The Doyle Log Rule

The Doyle Rule is a simple formula, which makes it popular. However, it is known to heavily underestimate the board footage of small logs and overestimate large ones.

Formula: BF = ((D - 4) / 4)^2 * L or more commonly written as BF = (D - 4)^2 * (L / 16)

The Scribner Log Rule

The Scribner Rule was created by drawing diagrams of the cross-section of logs and estimating how many 1-inch boards could be fit within the circle. It is generally more accurate than the Doyle rule but does not account for log taper.

Formula (Approximation): BF = (0.79 * D^2 - 2 * D - 4) * (L / 16)

The International 1/4-Inch Log Rule

This is widely considered the most accurate of the three rules, as it accounts for a standard taper of 1/2 inch for every 4 feet of length and a 1/4-inch saw kerf. The formula is more complex as it calculates volume in 4-foot sections.

Formula (Per 4-foot section): BF_per_4ft = (0.905 * (0.22 * D^2 - 0.71 * D))

Log Rule Variable Explanations

Variable	Meaning	Unit	Typical Range
BF	Board Feet	(bd. ft.)	Varies
D	Log Diameter (small end, inside bark)	Inches	8 – 40+
L	Log Length	Feet	8 – 24

Practical Examples

Example 1: A Standard Hardwood Log

• Inputs: Diameter = 20 inches, Length = 16 feet
• Results:
  • Doyle Rule: ((20 – 4)^2) * (16 / 16) = 256 bd. ft.
  • Scribner Rule: Approximately 280 bd. ft.
  • International 1/4″ Rule: Approximately 320 bd. ft.

This example clearly shows how the Doyle rule gives a lower estimate compared to the more accurate International 1/4″ rule for a typical log.

Example 2: A Smaller Pine Log

• Inputs: Diameter = 12 inches, Length = 12 feet
• Results:
  • Doyle Rule: ((12 – 4)^2) * (12 / 16) = 48 bd. ft.
  • Scribner Rule: Approximately 60 bd. ft.
  • International 1/4″ Rule: Approximately 70 bd. ft.

Here again, the difference is significant. A seller might prefer to buy using the Doyle scale, while a buyer would get a more realistic yield estimate from the International scale. For more examples, a good resource to check would be a lumber weight calculator.

How to Use This Board Foot Calculator

1. Measure Log Diameter: Measure the diameter of the log in inches at its smallest end, inside the bark. If the end is not perfectly round, take two measurements at 90 degrees to each other and average them.
2. Measure Log Length: Measure the length of the log in feet. Round down to the nearest whole foot.
3. Enter Values: Input these two numbers into the calculator fields.
4. Select Log Rule: Choose the desired log scaling rule from the dropdown menu. The calculator will automatically show the primary result for that rule and compare it against the others.
5. Interpret Results: The calculator displays the estimated board feet. Use the chart to visually understand how the different rules impact the final estimate.

Key Factors That Affect Board Feet Yield

The number you get from a formula is an estimate. The actual amount of lumber you can get from a log is affected by several real-world variables.

• Log Taper: Logs are wider at the base than at the top. Only the International rule directly accounts for this taper, which is why it’s more accurate.
• Saw Kerf: The thickness of the saw blade turns a portion of the log into sawdust. Thinner kerf blades yield more lumber.
• Defects: Knots, rot, cracks, and curves in the log will reduce the amount of usable, high-quality lumber. These must be accounted for by the scaler.
• Sawyer Efficiency: The skill of the sawmill operator in planning cuts makes a huge difference in maximizing yield and minimizing waste.
• Shrinkage: Lumber shrinks as it dries. The amount of shrinkage varies by wood species. Anyone using a woodworking project calculator should be aware of this.
• Board Thickness: The target thickness of the final boards affects the total board foot calculation.

Frequently Asked Questions (FAQ)

Why are there so many different log rules?

Over 95 log rules have been developed in North America. They were created in different regions and at different times to serve local needs, often before standardized methods were available. The Doyle, Scribner, and International rules are the three that remain in widespread use today.

Which log rule should I use?

The International 1/4-Inch rule is generally considered the most accurate and best reflects the actual lumber yield under optimal conditions. However, the Doyle rule is still widely used in the hardwood industry, particularly in the eastern and southern US. Always clarify which rule is being used when buying or selling logs.

How do I measure diameter on an uneven log?

Take the longest and shortest diameter measurements at the small end of the log, inside the bark, and average them.

What does “diameter inside bark” (DIB) mean?

It means you should not include the thickness of the bark in your diameter measurement, as the bark is not converted into lumber.

How does a log weight calculator relate to board feet?

A log weight calculator estimates the physical weight of a log, which is useful for transportation. Board feet, on the other hand, estimates the volume of usable lumber, which is useful for valuation and project planning.

Does log taper matter?

Yes, significantly. A log with a lot of taper (it gets much narrower from one end to the other) will yield less lumber than a log that is more cylindrical. The International rule is the only common formula that mathematically accounts for taper.

Why does my calculated board footage differ from the mill’s?

This can happen for many reasons: using a different log rule, deductions for defects (rot, sweep), or differences in sawyer efficiency and equipment. Communication with the mill is key.

Can I calculate board feet for a standing tree?

Yes, but it’s more complex. It involves measuring the diameter at breast height (DBH) and estimating the merchantable height. Special formulas and tables are used for this. To learn more about tree spacing and forest management, you might find a tree spacing calculator useful.

Related Tools and Internal Resources

Here are some other calculators and resources you might find useful:

• Lumber Weight Calculator: Estimate the weight of your sawn lumber for shipping and handling.
• Log Weight Calculator: Before you even get to board feet, determine the weight of a log for safe transport.
• Woodworking Project Calculator: Plan your next project by estimating the amount of wood you’ll need.
• Chainsaw Fuel Mix Calculator: Ensure your equipment is running perfectly with the correct fuel-to-oil ratio.
• Tree Spacing Calculator: For those managing forests, proper tree spacing is crucial for healthy growth.
• Stump Removal Cost Calculator: Estimate the cost of removing tree stumps after harvesting.