The most common definition of length is that it is the measurement of the extent of something along its greatest dimension. That, of course, is for physical entities. Length is also used to describe passing of time, but that is not covered here (unless you are measuring the length of a timeline chart).

Standard units = Meter (m) for metric, foot (ft) for English

	inch	foot	mile	centimeter	meter	kilometer
1 in =	1	8.333 * 10-2	1.578 * 10-5	2.540	2.540 * 10-2	2.540 * 10-5
1 ft =	12	1	1.894 * 10-4	30.48	0.304 8	3.048 * 10-4
1 mi =	6.336 * 104	5 280	1	1.609 * 105	160 9	1.609
1 cm =	0.393 7	3.281 * 10-2	6.214 * 10-6	1	10-2	10-5
1 m =	39.37	3.281	6.214 * 10-4	100	1	10-3
1 km =	3.93 7 * 104	3 281	0.621 * 104	105	1 000	1

 

Non-Standard Length Units Conversions

1 cable = 720 ft = 219.456 m

1 cable (U.K.) = 608 ft = 185.318 m

1 chain (engineers') = 100 ft = 30.48 m

1 chain (surveyors') = 66 ft = 20.117 m

1 fathom = 6 ft = 1.829 m

1 fermi = 10-15 m

1 furlong = 660 ft = 201.168 m

1 hand = 4 in = 0.101 6 m

1 league (nautical) = 3 nmi = 5 556 m

1 league (statute) = 3 stat mi

1 light year = 9.460 895 2 * 1015 m

1 link (engineers') = 1 ft = 0.304 8 m

1 link (surveyors') = 7.92 in = 0.201168 m

1 myriameter = 10 000 m

1 nautical mile (nmi) = 1 853.184 m

1 pale = 1 perch (linear) = 1 rod = 5.029 2 m

1 pica = 1/6 in (approx.) = 4.217 518 * 10-3 m

1 point = 1/72 in (approx.) = 3.514 598 * 10-4 m

1 span = 9 in = 0.228 6 m

1 astronomical unit (au) = 92 957 130.3 mi = 1.496 * 108 km

1 parsec = 1.917 378 44 * 1013 mi = 3.085 721 50 *1013 km