Measure the longest length and widest width of the tabletop with a tape measure. Taking measurements from the longest points of nonrectangular and odd-shaped tables ensures you will have enough epoxy to coat the entire table.
Multiply the width times the length -- in inches -- to determine the area of the tabletop in square inches. For example, a table measuring 72-inches-by-48 inches would equal 3,456 square inches.
Multiply the square inches by the decimal equivalent of the thickness of epoxy resin required for the table to determine the total volume of material needed in cubic inches. For example, a 1/8-inch thick layer of epoxy would have a decimal value of 0.125. Multiply 3,456 square-inches by 0.125 for 432 cubic inches.
Order enough epoxy resin to cover the total volume plus 10 percent for waste. For example, 432 cubic inches times 10 percent equals 475 cubic inches of epoxy to complete the tabletop finish without running short of material.