The MKS (meter-kilogram-second) system of units is part of the SI (Systeme Internationale) that is the standard in much of the world outside of the United States, and in science.

Length

• The meter was originally defined as 1/10⁷ of the distance from the equator to the North pole measured along a longitude passing through Paris.
• In 1899 it was defined as the length between two marks on a particular platinum-iridium rod kept in Paris.
• In 1960 the meter was redefined as 1,650,763.73 wavelengths of a particular orange light emitted by krypton-86.
• One meter is about the length of your stride.

Mass

• One kilogram is about 2.2 pounds.
• The standard kilogram is a particular platinum-iridium cylinder at the International Bureau of Weights and Measures near Paris.
• One litre of water has a mass of 1 kg.

Time

• The second is defined as the time required for 9,192,631,770 periods of the radiation emitted when an electron in a cesium atom makes a particular transition.
• One year = p x 10⁷ s
• Average human lifespan = 2 x 10⁹ s
• Age of the Universe = 10¹⁸ s

Exercise

Determine your height in meters and your mass in kilograms. Figure out how many seconds it took you to figure this out.