Measure the diameter of the small end of the log. Take the measurement inside the bark to the nearest inch with a tape measure. Take two measurements at right angles to each other and average the two measurements if the log is not round. Assume for this example that the diameter of the log is 14 inches.
Measure the length of the log to the nearest inch with a tape measure. Assume for this example that the log has a length of 238 inches.
Obtain the density of the wood in units of pounds per cubic foot, which varies greatly according to the type of wood. Assume for this example that you wish to known the weight of a American red oak log. This wood has a weight of 45 pounds per square foot.
Calculate the weight of the log with the formula M = P x (W/24) x (W/24) x L/12 x D. M is the weight of the log in pounds, P is the value of pi, W is the diameter of the log in inches, L is the length of the log in inches and D is the density of the log in pounds per square foot.
Assume for this example that W is 14 inches, L is 238 inches and D is 45 pounds per square foot. P is always 3.14. The weight of this log is therefore M = 3.14 x (14/24) x (14/24) x 238/12 x 45 = 954 pounds.