How to Measure the Angle of a Conical Hole
You can find the angle of a conical hole using a protractor and a ruler to get a sense of the steepness of the drop. A conical hole has the shape of the inside of a hollow cone just like looking into the bottom of an orange construction cone. The larger the angle between the inside surface of the hole and the ground, the more inclined the walls of the cone. A protractor is essential for measuring the conical hole angle accurately.
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Instructions
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Place the wooden dowel against the slanted interior surface of the conical hole. The dowel needs to be small enough to fit inside the hole.
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Stand and hold the protractor vertically with its flat side against the ground and directly behind the wooden dowel. Position the protractor so that the center of its flat side is above the point where the sloped wall of the hole meets the ground. Read the degree marking from the protractor that lies behind the wooden dowel. Be sure to use the scale on the protractor that begins farthest from the hole. This measurement is the angle the wall of the conical hole makes with the ground. For example, assume the angle is 70 degrees.
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Subtract the angle the walls of the conical hole make with the ground from 90 degrees. This result is half of the opening angle of the bottom of the conical hole. Completing this step, for the example, leads to 90 degrees minus 70 degrees, or a half-opening angle of 20 degrees.
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Multiply the half-opening angle by 2 to obtain the conical hole's opening angle. Completing the example, you have 20 degrees times 2, or an opening angle of 40 degrees.
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Tips & Warnings
Protractors have two degree marking scales. One is read from left to right and the other from right to left. Always read the scale that starts at the base of an angle.
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