To convert pounds to kilograms, divide the number of pounds by 2.2046. In the case of 136 pounds, this will be 136 divided by 2.2046, or 61.68856 kilograms. Pounds are used in the United States customary and imperial systems of measurement while kilometers are used in the metric system.
While the United States customary system and the imperial system are close enough that the average person can consider them to be interchangeable, there are slight differences between them that have a significant impact in areas like engineering where precision is necessary. For example, while 1 kilogram is equal to 2.2046 American pounds as can be surmised above, it takes 2.2046223 imperial pounds to equal the same amount. This discrepancy exists because both the imperial and Unites States customary systems are derived from the English system of measurement, which can trace its roots back to the Carolingian, Saxon and Ancient Roman systems of measurement.
To reconcile the two systems, an attempt was made in 1960 to create a new international pound and yard to be used by both the United States and the United Kingdom and Commonwealth countries. The new yard equaled .9144 meters, while the new pound equaled .45359237 kilograms. The U.K. approved the new system in 1963, while Canada adopted the system early in 1951, but the U.S. never ratified the treaty. The adoption of the metric system by the U.K and Commonwealth countries in the 1960s later made the new units largely pointless.