The Weather API includes a unitGroup parameter that controls the units of measurement used in the response. This article lists the units used for each supported unit group.
The four supported unit group IDs are:
us– United States customary unitsmetric– Metric unitsuk– United Kingdom mixed unitsbase– Base or scientific units
If you do not specify unitGroup, the API defaults to us.
For example, the following request returns temperatures in degrees Celsius, precipitation in millimeters, and wind speeds in kilometers per hour:
https://weather.visualcrossing.com/VisualCrossingWebServices/rest/services/timeline/London,UK?unitGroup=metric&key=YOUR_API_KEYThe unitGroup value is case-sensitive and must be one of the four IDs listed above. An unsupported value returns an error.
us – United States units
| Weather variable | Unit of measurement |
|---|---|
| Temperature, dew point, heat index, wind chill, and feels-like temperature | Degrees Fahrenheit (°F) |
| Precipitation | Inches |
| Precipitation rate | Inches per hour |
| Snow and snow depth | Inches |
| Wind speed and wind gust | Miles per hour |
| Visibility | Miles |
| Atmospheric pressure | Hectopascals (hPa), numerically equivalent to millibars |
| Wave and swell height | Feet |
| Hail size | Inches |
| Solar radiation | Watts per square meter (W/m²) |
| Solar energy | Megajoules per square meter (MJ/m²) |
metric – Metric units
| Weather variable | Unit of measurement |
| Temperature, dew point, heat index, wind chill, and feels-like temperature | Degrees Celsius (°C) |
| Precipitation | Millimeters |
| Precipitation rate | Millimeters per hour |
| Snow and snow depth | Centimeters |
| Wind speed and wind gust | Kilometers per hour |
| Visibility | Kilometers |
| Atmospheric pressure | Hectopascals (hPa), numerically equivalent to millibars |
| Wave and swell height | Meters |
| Hail size | Millimeters |
| Solar radiation | Watts per square meter (W/m²) |
| Solar energy | Megajoules per square meter (MJ/m²) |
uk – United Kingdom units
The uk unit group combines metric and imperial units commonly used in the United Kingdom. Temperatures and precipitation use metric units, while wind speed and visibility use miles.
| Weather variable | Unit of measurement |
| Temperature, dew point, heat index, wind chill, and feels-like temperature | Degrees Celsius (°C) |
| Precipitation | Millimeters |
| Precipitation rate | Millimeters per hour |
| Snow and snow depth | Centimeters |
| Wind speed and wind gust | Miles per hour |
| Visibility | Miles |
| Atmospheric pressure | Hectopascals (hPa), numerically equivalent to millibars |
| Wave and swell height | Meters |
| Hail size | Inches |
| Solar radiation | Watts per square meter (W/m²) |
| Solar energy | Megajoules per square meter (MJ/m²) |
base – Base or scientific units
| Weather variable | Unit of measurement |
| Temperature, dew point, heat index, wind chill, and feels-like temperature | Kelvin (K) |
| Precipitation | Millimeters |
| Precipitation rate | Millimeters per hour |
| Snow and snow depth | Centimeters |
| Wind speed and wind gust | Meters per second |
| Visibility | Kilometers |
| Atmospheric pressure | Hectopascals (hPa), numerically equivalent to millibars |
| Wave and swell height | Meters |
| Hail size | Millimeters |
| Solar radiation | Watts per square meter (W/m²) |
| Solar energy | Megajoules per square meter (MJ/m²) |
Values that do not change with the unit group
Some Weather API values are dimensionless or always use the same unit. These values are not affected by the unitGroup parameter.
| Weather variable | Unit or scale |
| Relative humidity | Percent (%) |
| Cloud cover | Percent (%) |
| Precipitation probability | Percent (%) |
| Precipitation coverage | Percent (%) |
| Wind, wave, and swell direction | Degrees from north (0–360°) |
| UV index | Index value |
| Solar radiation | Watts per square meter (W/m²) |
| Solar energy | Megajoules per square meter (MJ/m²) |
| Air-quality pollutant concentrations | Micrograms per cubic meter (µg/m³) |
| US and European air-quality indexes | Index value |
| Moon phase | Fraction from 0 to 1 |
| Severe-weather risk | Index value |
The unit group changes the units in which values are returned; it does not change the underlying weather data, location, date range, or response structure.