Determine the average pressure of the Earth's atmosphere at sea level. Express the pressure in mm Hg and in the familiar pounds (lbs) per square inch, as follows: 760 mm Hg = 14.69 lbs/square inch.
Divide both sides of the equation by 760 to convert mm Hg to lbs/inch squared: mm Hg = 14.69 lbs/inch squared x 760 = 0.0193 lbs/inch squared.
Set up a dimensional equation to convert mm Hg to kPa. Use the conversion factor in step 2:
mm Hg = (0.0193 lbs/inch squared) x 4.448 N/lb x (12 square inches squared/feet squared) x (feet squared/0.3048 squared meters squared) x (meters squared Pa/N) x kPa/1000 Pa. All the terms are conversion factors between physical quantities and each quantity is expressed in its basic physical dimensions. The physical dimensions of a quantity can be any combination of mass, length and time.
Cancel the physical terms in the numerators. Note that all the terms cancel out, except mm Hg and kPa. Multiply all the numbers in the numerators and divide the result by the product of the numbers in the denominators to arrive at the answer: 1 mm Hg = 0.1333 kPa.