How to Read a Doyle Log Scale Rule

The Doyle Log Scale allows you to estimate how much lumber a log will provide.
The Doyle Log Scale allows you to estimate how much lumber a log will provide. (Image: log image by Vladimir Karpenko from

The Doyle Log Scale Ruler is a mechanical device used by individuals who are cutting lumber. The ruler is used to measure both the diameter and the height of the log being cut. Using that information, and the scale ruler, the numbers can be converted to provide an estimate for how many viable pieces of wood can be procured from the log. The numbers provided are only an estimate; however, they can be useful for deciding how much wood must be cut to accommodate a project.

Place the Doyle Log Rule against the trunk of the tree 4 feet off the ground, and stand so that your eyes are at the height of the ruler and 25 inches away from it.

Adjust the left-to-right orientation of the ruler so that the left end of the ruler aligns with the left edge of the trunk from your vantage point 25 inches from the ruler.

Shift your line of sight to the right without moving your head, and note where the right side of the trunk passes behind the ruler from your vantage point. The edge will intersect with a diameter reading along the top of the ruler, which represents the approximate diameter of the tree. It is important to maintain the 25-inch distance and to keep your head stationary to maximize accuracy.

Stand 66 feet from the tree and hold the ruler vertically with the "Number of 16 Foot Logs" scale facing you.

Hold the ruler 25 inches from your eyes, and align the bottom of the ruler with the top of the stump of the tree. The stump ends where the tree first narrows from its roots to the size of the diameter for the trunk, approximately 1 foot above the ground.

Read the right side of the log scale ruler at the highest point at which the trunk is approximately 6 to 10 inches in diameter. The numbered lines represent full logs, 16 feet long, while the dashes without numbers between the numerals represent 8-feet-long half logs.

Consult the chart on the Doyle Log Scale Ruler and find the number in the grid that corresponds with the diameter found in Step 3 and the height found in Step 6.

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