How to Calculate Gallons Based on Dimensions
- 1). Find the appropriate volume formula for the geometric shape under investigation. For example, the volume of a cylinder is given by V = pi * r^2 * h, where pi = 3.1416, r^2 represents the square of the radius and h represents the cylinder's height.
- 2). Measure the dimensions of the object using a ruler or tape measure. Make certain to take the inside dimensions as opposed to the outside dimensions. For example, a cylinder open on one end may measure 1.0 inches at its outside diameter, but only 7/8 inches inside diameter. Similarly, the height of the cylinder may measure 6.5 inches outside but 6 3/8 inches inside.
- 3). Convert all measured dimensions into decimal form. For example, 3/8 inches represents 3 / 8, which equals 0.375. Therefore, a measured dimension of of 6 3/8 inches represents 6.375 inches, and 7/8 represents 0.875 inches.
- 4). Substitute the measurements of the container's dimensions into the appropriate formula for volume. Continuing the previous example, the volume for a cylinder is V = pi * r^2 * h. The radius of a circle is half the diameter, so r = 0.875 / 2 = 0.4375 inches. The volume then becomes V = 3.1416 * 0.4375^2 * 6.375 = 3.8334 cubic inches.
- 5). Convert the calculated interior volume of the container to gallons by multiplying the number of cubic inches by 0.004329. A volume of 3.8334 cubic inches, for example, converts to 0.0166 gallons.
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