If you are working with timber or planning to sell logs, one important question you may ask is how many board feet in a 20 inch log. This is a key measurement used in the lumber industry to estimate how much usable wood you can get from a log.
The answer is not always exact because it depends on the log length and the log rule used. However, with the right method, you can estimate board feet quickly and accurately.
In this guide, you will learn what a board foot is, how to calculate it, and how many board feet you can expect from a 20 inch log.
What Is a Board Foot
Definition
A board foot is a unit of measurement used for lumber. It represents a piece of wood that is:
1 foot long
1 foot wide
1 inch thick
So one board foot equals 144 cubic inches of wood.
Why It Matters
Board feet help buyers and sellers measure wood volume easily. It is widely used in sawmills, woodworking, and forestry.
How Many Board Feet in a 20 Inch Log
The number of board feet in a 20 inch log depends on two main factors:
Log length
Log rule used for calculation
A 20 inch diameter log can produce very different results depending on whether it is 8 feet, 10 feet, or longer.
Common Log Rules Explained
There are three main rules used to estimate board feet from logs. Each gives slightly different results.
Doyle Rule
This is the most commonly used rule in North America. It often underestimates small logs but is simple to use.
Scribner Rule
This rule is more accurate than Doyle and considers lumber layout more realistically.
International Rule
This is the most accurate method. It accounts for saw kerf and wood waste during cutting.
Example Calculation for a 20 Inch Log
Let’s look at real examples using common log lengths.
8 Foot Log Example
For a 20 inch diameter log that is 8 feet long:
Doyle Rule estimate: around 130 to 150 board feet
Scribner Rule estimate: around 160 to 180 board feet
International Rule estimate: around 180 to 200 board feet
10 Foot Log Example
For a 20 inch diameter log that is 10 feet long:
Doyle Rule estimate: around 180 to 200 board feet
Scribner Rule estimate: around 220 to 250 board feet
International Rule estimate: around 250 to 280 board feet
Board Feet Chart for 20 Inch Logs
Log Length | Doyle Rule | Scribner Rule | International Rule
8 ft | 140 | 170 | 190
10 ft | 190 | 235 | 265
12 ft | 240 | 290 | 330
These numbers are estimates and may vary slightly depending on log quality.
How to Calculate Board Feet Yourself
You can estimate board feet using formulas or log rule tables.
For example, the Doyle rule formula is:
(Diameter – 4) squared × length ÷ 16
So for a 20 inch log:
(20 – 4) squared = 16 × 16 = 256
Multiply by length and divide by 16
This gives you a rough estimate of board feet.
Factors That Affect Lumber Yield
Several factors influence how many board feet you actually get:
Log straightness
Knots and defects
Sawing method
Wood species
Moisture content
Even if two logs have the same size, their yield can be different.
Common Mistakes
Many beginners make errors when estimating board feet.
One mistake is ignoring the log rule used. Different rules give different results.
Another mistake is not measuring diameter correctly. Always measure inside bark for accuracy.
Some people also forget that not all wood in a log becomes usable lumber.
Expert Tips
Always use the same log rule when comparing prices.
Measure logs carefully and consistently.
Use charts for quick estimates instead of doing manual calculations every time.
Consider waste and defects when planning projects.
Benefits of Understanding Board Feet
Knowing how many board feet in a 20 inch log helps you:
Estimate wood value accurately
Plan woodworking projects
Avoid overpaying for logs
Improve efficiency in sawmill operations
FAQs
- How many board feet are in a 20 inch log?
It depends on length and log rule, but typically ranges from 140 to 300 board feet. - Which log rule is most accurate?
The International rule is considered the most accurate. - Does log length affect board feet?
Yes, longer logs produce more board feet. - Why do different rules give different results?
Each rule accounts for wood waste and cutting methods differently. - Can I calculate board feet without a chart?
Yes, you can use formulas like the Doyle rule, but charts are faster and easier.
Conclusion
So, how many board feet in a 20 inch log? The answer depends on the log length and the rule you use, but most estimates fall between 140 and 300 board feet.
By understanding board foot calculations and using the right method, you can accurately estimate lumber yield and make better decisions when buying or selling logs.
