Note: The charts do not display properly in Netscape 4.7 or earlier browsers, because those browsers are not compliant with the current W3C HTML standard.

 (B) yard foot 3 inch (A) 12 36 U.K., before 12th c – 1963 (C) 2.54cm 30.48cm 0.91438348m (D) (F) US, 1893-1959 (E)=100/3937cm = 1200/3937cm = 3600/3937m U.S., after 1959; U.K, after 1963 = 2.54cm = 30.48cm = 0.9144m

Each unit is represented by one column and one row. The column of the smallest unit is on the left. The taller the column, the bigger the unit.

(A) The number in the box tells how many of the row unit are in the column unit. Here, 12 inches in a foot.

(C) The bottom rows of the chart, with a white background and green type, contain equivalents to the column's unit in SI units and sometimes also in U. S. customary units. Here, 1 inch is 2.54 centimeters. Some cautions:

• All the units in a chart measure the same property, in this example, length. But a particular term may be the name of several different units that measure different things. That a unit name appears in one chart doesn't mean that that term doesn't also appear in another chart with a different meaning.
• (D) On some charts, the equivalent for one unit has many more decimal places than the others. In many cases, this indicates this is the equivalence from which the other equivalences were calculated. Often, it is an equivalence arrived at by a physical comparison of standards.
• In a single row equivalents may be given in several different units. For example, as the units described get bigger the equivalents may go from millimeters to centimeters to meters to kilometers. Watch out for these changes!
• (E) If an equals sign appears, the conversion is exact, that is, by definition. In this case, in 1893 the United States redefined its yard in terms of the meter.

(F) Often the same set of ratios between units was used with different values for the units. For example, in this case the length of the yard has changed, but 3 feet in a yard has not. In such cases, for the more important systems, more than one row of equivalences may be provided.

The charts are offered as a way of showing relationships between units, not to provide conversion factors. The conversion information presented in the charts IS NOT EXHAUSTIVE.

• There isn't enough space in the charts to provide as many decimal places in the equivalence as may have been measured. The page for the unit may have a more precise value.
• There isn't enough space on the charts to show all the magnitudes used in different times and places. Only the most important are shown. Again, see the page on a unit for other values for other times and places.