How to Calculate Board Feet on a Log

Written by john woloch
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How to Calculate Board Feet on a Log
Foresters express the amount of lumber in a log using board feet. (Jupiterimages/Photos.com/Getty Images)

When American poet Joyce Kilmer looked at a tree, he saw beauty. When a forester looks at a tree, he probably sees board feet. Board feet is a convenient unit of measurement for lumber. It is commonly used to express the approximate amount of lumber in logs and standing timber. Given the importance of trees and the lumber that comes from them, it's not surprising that there is more than one way of measuring board feet.

Skill level:
Moderately Easy

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Things you need

  • Tape measure
  • Calculator

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Instructions

    Scribner Log Rule

  1. 1

    Measure the diameter of the small end of the log using a tape measure and express the answer in inches. For example, the diameter of the small end of a log is 10 inches.

  2. 2

    Measure the length of the log using a tape measure and express the answer in feet. For example, the length of the log is eight feet.

  3. 3

    Square the diameter of the log and multiply it by 0.79 using a calculator. For example, (10 x 10) x 0.79 = 79.

  4. 4

    Subtract the product of 2 and the diameter of the log from your answer. For example, 79 - (2 x 10) = 59.

  5. 5

    Subtract 4 from your answer. For example, 59 - 4 = 55.

  6. 6

    Multiply your answer times the quotient of the length of the log divided by sixteen. For example, 55 x (8 / 16) = 27.5. There are approximately 27.5 board feet in the log according to the Scribner Log Rule.

    Doyle Log Rule

  1. 1

    Measure the diameter of the small end of the log using a tape measure and express the answer in inches. For example, the diameter of the small end of a log is 10 inches.

  2. 2

    Measure the length of the log using a tape measure and express the answer in feet. For example, the length of the log is eight feet.

  3. 3

    Divide by 4 the difference of the log diameter and 4. For example, (10 - 4) / 4 = 1.5.

  4. 4

    Square your answer. For example, 1.5^2 = 2.25.

  5. 5

    Multiply your answer times the length of the log. For example, 2.25 x 8 = 18. There are approximately 18 board feet in the log according to the Doyle Log Rule.

    International Log Rule for Eight-foot Logs

  1. 1

    Measure the diameter of the small end of an eight-foot log using a tape measure and express the answer in inches. For example, the diameter of the small end of an eight-foot log is 10 inches.

  2. 2

    Square the log diameter and multiply the answer times 0.44. For example, (10 x 10) x 0.44 = 44.

  3. 3

    Subtract from your answer the product of 1.20 and the diameter. For example, 44 - (1.20 x 10) = 32.

  4. 4

    Subtract from your answer 0.30. For example, 32 - 0.30 = 31.7. There are approximately 31.7 board feet in the log according to the International Log Rule.

    International Log Rule for All Logs

  1. 1

    Use the appropriate International Log Rule for log lengths other than eight feet. Using "D" as log diameter in inches, and "BF" as board feet, these rules are

    4-foot logs: BF = 0.22D^2 - 0.71D

    8-foot logs: BF = 0.44D^2 - 1.20D - 0.30

    12-foot logs: BF = 0.66D^2 - 1.47D - 0.79

    16-foot logs: BF = 0.88D^2 - 1.52D - 1.36

    20-foot logs: BF = 1.10D^2 - 1.35D - 1.90

  2. 2

    Treat logs longer than 20 feet as made up of logs of International Rule lengths. For example, if you have a 36-foot log, treat it as one 16-foot log and one 20-foot log.

  3. 3

    Use the equation BF = 0.88D^2 - 1.52D - 1.36 for the 16-foot section of the 36-foot log. Assume the narrow end of this section has a diameter of 10 inches. For example, 0.88 x (10 x 10) - (1.52 x 10) - 1.36 = 71.44. There are approximately 71.44 board feet in the 16-foot section of the log.

  4. 4

    Use the equation BF = 1.10D^2 - 1.35D - 1.90 for the 20-foot section of the 36-foot log. Assume the narrow end of this section has a diameter of 20 inches. For example, 1.10 x (20 x 20) - (1.35 x 20) - 1.90 = 411.1. There are approximately 411.1 board feet in the 20-foot section of the log.

  5. 5

    Add the board feet of each measured section of the log. For example, 71.44 + 411.1 = 482.54. There are approximately 482.54 board feet in the 36-foot log according to the International Log Rule.

Tips and warnings

  • The log rules often give different results because they make different allowances for log taper, the spacing and arrangement of boards within the log, and the assumed width of the saw's kerf, or cut.
  • The Doyle Log Rule is most accurate for logs with a diameter between 26 and 36 inches.
  • If you must use the International Rule more than once, you can estimate the diameter of a given small section of the log by measuring the circumference of the section and dividing your measurement in inches by 3.14.

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