The metric SI System (Le Système International d'Unités)

Over 1000 conversion units are split over 16 pages for faster loading. The Detail Pages, as listed in the menu, cover topics in greater depth.

Select with the first letter of the unit from the jump-menu below - so if you want acres, click on the a link below then look on the page that opens for acres

For metric conversions go to a unit starting with -
a b c d e f g h i j k l m n o p q r s t u v w y

Other pages on this site describe the metric prefixes like kilo which is Greek for 1000 and was introduced to the metric system by the French in 1795. The prefixes are like a multiplier of the unit that follows. So a kilometre is 1000 metres and a centimetre is a hundreth of a metre. Note that milli means a thousandth NOT a millionth.

Learn and remember the prefixes and look for the unit root. Most people have heard of decibels for measuring sound - a decibel is a tenth of a bel - the bel is the base unit for sound. Similarly, millibars is commonly used by weather forecasters measuring atmospheric pressure, and millibars are a fraction (1/1,000th) of the base unit - bar. Prefixes are a simple and powerful tool.

The basic units for length, mass, etc. are defined here and then those basic units are used to describe a host of other units derived from those basic units.

In addition to unit conversions we have added practical conversion tables such as density and specific gravity of substances, structural and electrical wire gauge, clothing, threads and, before we forget, a page on Standard Imperial units.
Make use of your browser's search facility (Ctrl+F or Edit>Find) to find obscure units on our pages.

With all conversions you must be attempting to convert equal units - length to length, mass to mass, etc. You cannot convert metres to pounds just as you cannot convert feet to pounds. Look up one of the units in the tables and see what it usually converts to.

Example of reversing the formula :-
Task: How many sq.rods in 10 acres.
From the tables: 1 acre = 160 sq.rods, so
10 acres x 160 = 1600 sq.rods
When you want to reverse the conversion,
divide by the factor viz.
1600 sq.rods/160 = 10 acres

Read the note at the bottom of most pages on Scientific Notation. This is like a shorthand for writing very big or very small numbers. So 1.386E+12 is the same in shorthand as 1,386,000,000,000 in longhand - move the decimal point 12 spaces to the right, filling in zeros as needed.

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We have tried to be accurate with the information on our web site but cannot be held responsible for inaccuracies.
Go back to first principals and double check your calculations if the result is 'mission critical'.