Weather API unit systems

You can choose from METRIC or IMPERIAL for all Weather API endpoints.

To request a unit system, set units_system to METRIC or IMPERIAL. No units_system specified will default to METRIC.

https://weather.googleapis.com/v1/currentConditions:lookup?key=YOUR_API_KEY&location.latitude=LATITUDE&location.longitude=LONGITUDE&units_system=IMPERIAL

Weather API values changed from METRIC to IMPERIAL units

The following table lists the Weather API response values that can be converted between unit systems.

Unit Conversion (Metric to Imperial)	Weather API Values
Celsius (°C) to Fahrenheit (°F)	Temperature, Feels Like, Dew Point, Heat Index, Wind Chill, Wet Bulb
Millimeters (mm) to Inches (in)	Precipitation, QPF, Ice Thickness
Kilometers/hour (km/h) to Miles/hour (mph)	Wind Speed, Wind Gust
Kilometers (km) to Miles (mi)	Visibility

Note: Air Pressure (mb) is not converted to PSI.

Example for currentConditions response

The following table lists values included in the response body of a currentConditions request. Values in bold blue have changed from METRIC to IMPERIAL units:

Weather API feature	METRIC (default)	IMPERIAL
Current Time	2025-03-06T11:08:49.126979608Z	3/6/2025, 6:08:49 AM
Time Zone	America/New_York	America/New_York
Is Daytime	FALSE	FALSE
Weather Description	Mostly cloudy	Mostly cloudy
Temperature	11.5 °C	52.7 °F
Feels Like	9.9 °C	49.7 °F
Dew Point	8.7 °C	47.6 °F
Heat Index	11.5 °C	52.7 °F
Wind Chill	9.9 °C	49.7 °F
Relative Humidity	83 %	83 %
UV Index	0	0
Precipitation Probability	9 %	9 %
Precipitation	0 mm	0 in
Thunderstorm Probability	0	0
Air Pressure	991.47 mb	991.47 mb
Wind Direction	275 °	275 °
Wind Direction (Cardinal)	WEST	WEST
Wind Speed	14 km/h	9 mph
Wind Gust	27 km/h	17 mph
Visibility	10 km	6 mi
Cloud Cover	65 %	65 %
Temperature Change	1.4 °C	2.6 °F
Max Temperature	13.2 °C	55.8 °F
Min Temperature	10.1 °C	50.1 °F
QPF	27.5564 mm	1.0849 in

Units systems in the world

Unit systems by country

Most countries outside of the United States use the METRIC system, while the United States uses the IMPERIAL system. Some countries, such as the United Kingdom and Canada, use a hybrid of both systems. For a map and full list of countries that use the metric system, see Metrication.

Convert units from Weather API response

Convert units manually

You can convert units manually using the following script:

function convert(conversionType, value) {
  if (value === null || value === undefined || typeof value !== 'number') {
    return "Invalid input"; // Handle null, undefined, or non-numeric input
  }

  switch (conversionType) {
    case 'C_to_F': // Celsius to Fahrenheit
      let convertedCtoF = (value * 9 / 5) + 32;
      return convertedCtoF.toFixed(2) + " °F";
    case 'mm_to_in': // Millimeters to Inches
      let convertedMmToIn = value * 0.0393701;
      return convertedMmToIn.toFixed(2) + " in";
    case 'km_to_mi': // Kilometers to Miles
      let convertedKmToMi = value * 0.621371;
      return convertedKmToMi.toFixed(2) + " mi";
    case 'km/h_to_mph': // Kilometers per hour to Miles per hour
      let convertedKmHToMph = value * 0.621371;
      return convertedKmHToMph.toFixed(2) + " mph";
    case 'millibar_to_psi': // Millibar to PSI
      let convertedMillibarToPsi = value * 0.0145038;
      return convertedMillibarToPsi.toFixed(2) + " psi";
    default:
      return "Invalid conversion type";
  }
}

console.log(convert('C_to_F', 10)); // Output: 50.00 °F
console.log(convert('mm_to_in', 25)); // Output: 0.98 in
console.log(convert('invalid_type', 5)); // Output: Invalid conversion type

Convert units using a library

You can also use a library such as convert-units to convert units:

// module

import convert from 'convert-units';

// or script inclusion
//   <script src="https://unpkg.com/convert@5.8.0/dist/index.js" ></script> 
// let convert = convert.convert

function convertWithLibrary(conversionType, value) {
  if (value === null || value === undefined || typeof value !== 'number') {
    return "Invalid input";
  }

  try {
    switch (conversionType) {
      case 'C_to_F':
        let convertedCtoF = convert(value, 'C').to('F');
        return convertedCtoF.toFixed(2) + " °F";
      case 'mm_to_in':
        let convertedMmToIn = convert(value, 'mm').to('in');
        return convertedMmToIn.toFixed(2) + " in";
      case 'km_to_mi':
        let convertedKmToMi = convert(value, 'km').to('mi');
        return convertedKmToMi.toFixed(2) + " mi";
      case 'km/h_to_mph':
        // km/h is not directly supported, so we convert km to mi
        // then assume it's per hour
        let convertedKmToMiValue = convert(value, 'km').to('mi');
        return convertedKmToMiValue.toFixed(2) + " mph";
      case 'millibar_to_psi':
        // millibar is not directly supported, so convert millibar to bar, then bar to psi
        let barValue = value / 1000;
        let convertedMillibarToPsi = convert(barValue, 'bar').to('psi');
        return convertedMillibarToPsi.toFixed(2) + " psi";
      default:
        return "Invalid conversion type";
    }
  } catch (error) {
    console.error("Conversion error:", error);
    return "Conversion failed";
  }
}

console.log(convertWithLibrary('C_to_F', 10)); // Output: 50.00 °F
console.log(convertWithLibrary('mm_to_in', 25)); // Output: 0.98 in
console.log(convertWithLibrary('invalid_type', 5)); // Output: Invalid conversion type