Pounds per square foot, or psf, and pounds per square inch, or psi, are measurements of pressure still used in the United States but largely abandoned elsewhere in the world. One pound per square inch is equal to one pound-force exerted over 1 square inch of area. One pound per square foot is defined as 1 pound-force exerted over an area of 1 square foot. Since 1 square foot is 12 inches by 12 inches, or 144 square inches, 1 pound per square inch equals 144 pounds per square foot. Conversely, 1 pound per square foot equals 0.0069444 pounds per square inch.

Write the formula for converting pounds per square foot to pounds per square inch as pounds per square foot divided by 144 equals pounds per square inch (psi = psf ÷ 144).

Write the number of pounds per square foot to be converted.

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Divide the number of pounds per square foot by 144. The quotient is the pounds per square inch. For example, 2,160 pounds per square foot converts to 15 pounds per square inch (2160 psf ÷ 144 = 15 psi).