Map features/Units

Some tags have measurable values. The unit of such a value can be given explicitly as part of the value (e.g. maxspeed=50 mph). If no unit is specified, a default unit will be assumed (e.g. for maxspeed=50, the unit kilometre per hour is assumed). If the unit is different from the default, e.g. in non-metric countries, stating a unit is obligatory.

This article shows which units can be explicitly specified and which default units are implicitly assumed.

Default units

If no unit is explicitly specified, the following units are assumed:

Measure	Default unit	Implicit specification	Example
Distance over land	kilometre (kilometer)	km	distance=5 means a distance of 5 kilometres
Distance over water (ocean)	nautical mile	nmi	seamark:light:range=3 means a distance of 3 nautical miles
Duration	minute	minutes	duration=35 means a duration of 35 minutes
Siren range	metre (meter)	m	siren:range=600 means a siren audible over a 600-metre-radius area
Flow rate	cubic metre per second	m³/s	flow_rate=600 means a flow rate of 600 m³/s
Frequency	hertz	Hz	frequency=50 means a 50 Hz wire
Height	metre (meter)	m	ele=20 means an elevation of 20 metres;height=10 means an height of 10 metres
Length	metre (meter)	m	length=10 means a length of 10 mètres and width=3 means a width of 3 metres
Length (small-scale)	millimetre	mm	gauge=1435 means a standard gauge of 1435 millimetres
Pressure	bar	bar	pressure=86.2 means a pressure of 86.2 bars
Speed	kilometres per hour	km/h	maxspeed=100 means a speed limit of 100 kilometres per hour
Weight	tonne (metric ton)	t	maxweight=3.5 means a weight limit of 3.5 tonnes (3500 kg)
Voltage	volt	V	voltage=15000 means a 15 kV wire
Volumes	cubic metre	m³	volume=15 means a 15 m³ volume

Explicit specifications

The following units can be explicitly specified by adding them after the numeric value, separated by a space (with the exception of the combined specification of feet and inches):

Measure	Explicit specification	Unit	Example	Aliases (highly discouraged)	Conversion to default unit	Usage
Colour temperature	K	kelvin	light:colour=3500 K		1
Distance, height, or length	m (default)	metre (meter)	height=3 m	metre, metres, meter, meters	1	[1]
	km	kilometre (kilometer)	width=0.2 km	kilometre, kilometres, kilometer, kilometers	Multiply by 1000 or divide by 0.001	[2]
	mi	mile	width=1.45 mi	mile, miles	Multiply by 1609.344 or divide by 0.000621371192	[3]
	nmi	nautical mile	distance=6 nmi	international nautical mile	Multiply by 1852	[4]
	<feet>'<inch>"	feet and inches combined	maxwidth=12'5"	ft in	Multiply the feet by 12, add the inches and multiply the result by 0.0254
Duration	seconds	second	interval=45 seconds	second, s	Divide by 60
	minutes (default)	minute	maxstay=15 minutes	minute, min, m	1
	hours	hour	maxstay=2 hours	hour, h	Multiply by 60
	days	day	maxstay=3 days	day, d	Multiply by 1 440
	weeks	week	maxstay=2 weeks	week, w	Multiply by 10 080
	<hours>:<minutes>		duration=00:35
	ISO 8601 duration	ISO 8601 § Durations	duration=PT35M
Flow rate, volume	m³/s (default)	cubic metre per second	flow_rate=600 m³/s	m3/s	1
	m³/h	cubic metre per hour	flow_rate=80 m³/h	m3/h	Divide by 3 600
	l/min	litre per minute	flow_rate=600 l/min	L/min	Divide by 60 000
Frequency	Hz (default)	hertz	frequency=50 Hz		1
	kHz	kilohertz	frequency=423 kHz		Multiply by 1 000
	MHz	megahertz	frequency=88.0 MHz		Multiply by 1 000 000
Incline	%	grade	incline=10%		1
	°	degree of arc	incline=5.71°	º	1
Luminous flux	lm	lumen	light:flux=800 lm		1
Power	W	watt	generator:output:electricity=50 W		1
	kW	kilowatt	generator:output:electricity=50 kW		1
	MW	megawatt	generator:output:electricity=50 MW		1
	GW	gigawatt	generator:output:electricity=50 GW		1
Speed	km/h (default)	kilometres per hour	minspeed=80 km/h	kph, kmh, kmph	1	[5]
	mph	miles per hour	maxspeed=60 mph		Multiply by 1.609344	[6]
	knots	knots	maxspeed=10 knots		Multiply by 1.852	[7]
Weight	t (default)	tonne (metric ton)	maxweight=3 t		1	[8]
	kg	kilogram (kilogramme)	maxweight=3500 kg		Divide by 1000	[9]
	st	short ton (2,000 pounds)	maxweight=17 st	ST, T, ton, tons	Multiply by 0.9071847	[10]
	lt	long ton (2,240 pounds)	maxweight=12 lt		Multiply by 1.016047	[11]
	lbs	pound-mass	maxweight=7000 lbs	lb	Multiply by 0.00045359237	[12]
	cwt	long hundredweight	maxweight=30 cwt		Multiply by 50.80, and divide the result by 1000	[13]
Volume	m³ (default)	cubic metre	water_tank:volume=3 m³		1
	l	litre (litre)	volume=3500 l		Divide by 1000

Unusual keys

The following keys do not accept the standard syntax for units described above:

• depth=* – metres only, no provision for feet and inches
• ele=*, ele:min=*, ele:max=* – metres only, no provision for feet and inches except as a colon-delimited subkey; see the proposal to eliminate this exception
• railway:position=* – requires miles to be prefixed by mi:
• seamark:distance_mark:distance=* – uses seamark:distance_mark:units=* to specify the unit

Common mistakes

The following table presents examples of incorrect or discouraged tag usage together with their correct notation.

Incorrect usage	Explanation	Correct usage
height=6m	Missing space between numeric value and unit.	height=6 m
maxweight=3,5	Comma used as decimal separator.	maxweight=3.5
width=12' 6"	There should be no space between the specification of feet and inches.	width=12'6"
maxspeed=50 kph	Usage of an alias.	maxspeed=50 km/h

Notes

The precision of a measurement entered into OSM should match the precision of the source. For example, a "max width = 3.01m" sign should be recorded as maxwidth=3.01 (not maxwidth=3) and a "max height = 12 ft" sign should be recorded as maxheight=12' (not maxheight=12'0"). Data consumers should take care when converting between non-default and default units (e.g., mph to km/h) to maintain sensible precision.

See also

• Category:Units for a list of related tags and pages
• Units of measurement on Wikipedia
• Sophox query for the world's total electrical output – demonstrating how to convert units on the fly when querying OSM