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Petroleum Extension-The University of Texas at Austin
Units of Measurement

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hroughout the world, two systems of measurement domi-
Tnate: the English system and the met ric system. To day, the United
States is one of only a few countries that employs the En glish sys tem.
The English system uses the pound as the unit of weight, the foot as
the unit of length, and the gallon as the unit of capacity. In the En glish
system, for example, 1 foot equals 12 inches, 1 yard equals 36 inches,
and 1 mile equals 5,280 feet or 1,760 yards.
The metric system uses the gram as the unit of weight, the metre
as the unit of length, and the litre as the unit of capacity. In the metric
system, 1 me tre equals 10 decimetres, 100 centimetres, or 1,000 milli-
metres. A kilometre equals 1,000 me tres. The metric system, un like the
English system, uses a base of 10; thus, it is easy to convert from one unit
to another. To convert from one unit to an other in the English system,
you must memorize or look up the val ues.
In the late 1970s, the Eleventh General Conference on Weights and
Measures de scribed and adopted the Système International (SI) d’U nités.
Conference participants based the SI system on the metric system and
de signed it as an interna tional stan dard of measurement.
The Rotary Drilling Series gives both English and SI units. And
because the SI sys tem employs the British spelling of many of the terms,
the book follows those spelling rules as well. The unit of length, for ex-
ample, is metre, not me ter. (Note, however, that the unit of weight is
gram, not gramme.)
To aid U.S. readers in making and understanding the conversion
to the SI system, we in clude the following table.

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