# Map features/Units

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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 sea nautical mile `nmi` seamark:light:range=3 means a distance of 3 nautical miles
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
Length metre (meter) `m` 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

## 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
Distance, Height, or Length
`m` metre (meter) height=3 m metre, metres,
meter, meters
N/A 
`km` kilometre (kilometer) width=0.2 km kilometre, kilometres,
kilometer, kilometers
Multiply by 1000 or divide by 0.001 
`mi` mile width=1.45 mi mile, miles Multiply by 1609.344 or divide by 0.000621371192 
`nmi` nautical mile distance=6 nmi international nautical mile Multiply by 1852 
<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
Flow rate
`m³/s` cubic metre per second flow_rate=600 m³/s `m3/s` N/A
`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` hertz frequency=50 Hz N/A N/A
`kHz` kilohertz frequency=423 kHz N/A Multiply by 1 000
`MHz` megahertz frequency=88.0 MHz N/A Multiply by 1 000 000
Incline
`%` grade incline=10% N/A N/A
`°` degree of arc incline=5.71° `º` N/A
Power
`W` watt generator:output:electricity=50 W N/A N/A
`kW` kilowatt generator:output:electricity=50 kW N/A N/A
`MW` megawatt generator:output:electricity=50 MW N/A N/A
`GW` gigawatt generator:output:electricity=50 GW N/A N/A
Speed
`km/h` kilometres per hour minspeed=80 km/h kph, kmph N/A 
`mph` miles per hour maxspeed=60 mph Multiply by 1.609344 
`knots` knots maxspeed=10 knots Multiply by 1.852 
Weight
`t` tonne (metric ton) maxweight=3 t N/A 
`kg` kilogram (kilogramme) maxweight=3500 kg N/A Divide by 1000 
`st` short ton maxweight=17 st N/A Multiply by 0.9071847 (2,000 pounds actual weight) 
`lt` long ton maxweight=12 lt N/A Multiply by 1.016047 (2,240 pounds actual weight) 
`lbs` pound-mass maxweight=7000 lbs lb Multiply by 0.00045359237 
`cwt` long hundredweight maxweight=30 cwt N/A Multiply by 50.80 

## 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 and references

1. The symbol "cwt" is ambiguous: in the United States, it refers instead to the short hundredweight of 100 pounds (45 kg). However, this unit is only tagged in OSM according to standard signs in Guernsey and outdated signs in the United Kingdom, whereas hundredweight measurements have seldom if ever been signposted in the United States.