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Factors for Converting Units of Length This page contains a number of useful equivalences and conversion factors which can be used to equate the many units of measurement. Some are from a previous era and are rarely used to-day, but are interesting and useful if consulting old publications. When measuring, the metric system is the easiest to use since all smaller divisions are factors of 10. Workable lengths are nearly always quoted in millimetres (mm), eg. the standard kitchen unit or appliance is 600mm. The calculator below can be dragged around with your mouse for working out your conversion. Remember, to avoid mistakes measure twice and cut once! Although your error may not be as important as the one made when grinding the mirror for the Hubble Space Telescope. The measurement was small involving a few micrometres, but the cosequences were great, requiring additional optics to correct the focus and the resolution is still not what was intended.

Use these links to other pages of conversion factors.

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Calculator floats on page drag and operate with mouse. One operation at a time, for chain calculations clear result and re-enter for next stage.

Useful Length Relationships

1 inch (in,") = 1/12th of a foot = 1/36th of a yard
1 link = 7.92 inches
1 foot (ft, ')= 12 inches = 1/3rd of a yard = 1/5280th of a mile = 0.3048 metre
1 rod = 1 pole = 1 perch = 25 links = 5 ½ yards = 5.0292 metres
1 chain = 4 rods = 4 perch = 22 yards = 20.117 metres
1 furlong (furrow long) = 10 chains = 220 yards = 201.17 metres
8 furlongs = 1 mile
1 mile = 63360 inches = 5280 feet = 1760 yards = 80 chains = 1.6093 kilometre

The chain was a measuring instrument made up of 100 links, each 7.92 inches long making 66 feet or 22 yards.
The league is an old international measurement but has different values depending on the country. It was the distance between marker stones placed on roads. The English league is 3 statute miles; the French and Spanish league varies between localities, but is about 2.5 and 4.2 miles respectively. The metric league is 4 kilometres.

To give an indication of the possible origins of linear measurements:-
3 barleycorns = 1 inch
2¼ inches = 1 nail
3 inches = 1 palm
4 inches = 1 hand (used for the height of horses)
9 inches = 1 span
18 inches = 1 cubit
2½ feet = 1 military pace
5 feet = 1 geometrical pace.

Nautical Measure - The fathom is a nautical and mining measurement based on the space to which a man can extend his arms.
one fathom = 6 feet.
120 fathoms = 1 cable's length.
1 nautical mile or knot (international) = 2,02666 yards = 1.8532 kilometres.
3 knots = 1 league (nautical)
60 knots = 69.121 statute miles = 1 degree
360 degrees = the earth's circumference.

Circular Measure - Used in astronomical and geographical calculations
60 seconds = 1 minute (')
60 minutes = 1 degree (°)
30 degrees = 1 sign (zodiac)
60 degrees = 1 sevtant
90 degrees = 1 quadrant
360 degrees = 1 circle.

Length Conversion Factors

from	to	multiply by
inches (in)	millimetres (mm)	25.4
millimetres (mm)	inches (in)	0.03937
inches (in)	centimetres(cm)	2.54
centimetres(cm)	inches (in)	0.3937
feet (ft)	metres(m)	0.3048
metres (m)	feet (ft)	3.2808
metres (m)	yards (yd)	1.0936
yards (yd)	metres (m)	0.9144
kilometres (km)	miles	0.6214
miles	kilometres (km)	1.60934

For a less accurate mental reckoning the following can be used:-

metres to yards	add 1/10th
yards to metres	subtract 1/10th
kilometres to miles	multiply by 5 and divide by 8
miles to kilometres	multiply by 8 and divide by 5

Imperial to Metric Length Equivalences

inches	=	cm		cm	=	inches
1	=	2.54		1	=	0.39
2	=	5.08		2	=	0.79
3	=	7.62		3	=	1.18
4	=	10.16		4	=	1.58
5	=	12.7		5	=	1.97
6	=	15.24		6	=	2.36
7	=	17.78		7	=	2.76
8	=	20.32		8	=	3.15
9	=	22.86		9	=	3.54
10	=	25.4		10	=	3.94
11	=	27.94		15	=	5.91
12	=	30.48		20	=	7.87
15	=	38.1		25	=	9.84
20	=	50.8		30	=	11.81

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