# 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 an 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
Gauge Millimetre `mm` gauge=1435 means a standard gauge of 1435 millimetres
Height Metre (meter) `m` ele=20 means an elevation of 20 metres
Length Metre (meter) `m` width=3 means a width of 3 metres
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 

## 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