Select a sample location, which offers a tree density similar to the rest of the location.
Measure a circular sample plot 52 feet in diameter. The easiest way to do this is to have a helper hold the tape measure in the center of the plot, and extend the tape measure to 26 feet. Walk in a circle with the tape measure extended. You will have to negotiate around trees, but ultimately, you mark off a circle 52 feet in diameter. This sample plot represents roughly 1/20 of an acre.
Close one eye and extend the tape measure horizontally between both out-reached hands, while barely touching the tape measure against one of the trees in the plot. Visually align the "zero" mark of the tape measure with one edge of the tree. Read the measurement of the other edge of the tree to record its diameter in inches.
Divide the diameter by two to calculate the radius. Square the radius, and then multiply it by pi, 3.14, to calculate the basal area of the tree. As an example, a 10-inch diameter tree would have a basal area of 78.5 square inches.
Repeat the diameter measurement and basal area calculation for every tree in the plot. For simplicity, ignore saplings, since these do not contribute to the timber harvest.
Add all the basal areas calculations together to calculate the total plot basal area. As an example, if you had 20 trees that measured 78.5 square inches in diameter, then the total plot basal area is 1,570 square inches.
Divide the total sample basal area by 144 to convert to square feet. In the example, the total plot basal area is converted to 10.9 square feet.
Multiply the total plot basal area by 20 to calculate density in basal area per acre. In the example, 10.9 times 20 gives you a density of 218 square feet per acre.
Multiply the density by the total area of the location to calculate total basal area. In the example, if the total location area was 15 acres, then you multiply 218 by 15, which equals 3,270 square feet per acre.