If the Free T3 is in the pg/ml unit, you must multiply the result by 100 to convert pg/ml into pg/dl i.e 3.25 pg/ml = 325 pg/dl. The Reverse T3 must be in ng/dl (normal unit in U.S.) i.e. 17 ng/dl. The ratio is calculated by dividing the Free T3 result by the Reverse T3 result, i.e. 325 / 17 = 19.