Modern mobile applications frequently display physical measurements, ranging from weather temperatures and driving distances to culinary recipes and parcel weights. While individual apps sometimes provide dedicated toggles, iOS includes a centralised system-level setting that defines your preferred measurement standards across the entire operating system and all compatible third-party applications.
Configuring this preference ensures that Apple Maps, Weather, Health, Fitness, and integrated safari web applications automatically render data in units that feel intuitive to you, whether you rely on the Metric system, US customary units, or the blended UK measurement framework.
Understanding the iOS Measurement System Hierarchy
Apple categorises measurement preferences into three standardised profiles within the regional configuration engine:
- Metric: Prioritises Celsius for temperature, metres and kilometres for distance, grams and kilograms for mass, and millilitres or litres for liquid volume. This standard is universally adopted across continental Europe, Asia, and most international scientific domains.
- US Customary: Standardises Fahrenheit for temperature, feet and miles for travel distance, ounces and pounds for mass, and fluid ounces, pints, and gallons for liquid volume.
- UK (United Kingdom): Implements the customary British blend, utilising Celsius for temperature, miles and yards for road transit distances, and metric units (grams, kilograms, and litres) for everyday consumer weights and trade measures.
When you modify this setting, native iOS apps immediately recalculate and convert displayed values without altering the raw underlying data stored in your personal records.
How to Change the Measurement System in iPhone Settings
To switch between Metric, US, and UK measurement frameworks across your iPhone, follow these straightforward steps:
- Open the Settings app on your iPhone.
- Scroll down and tap General.
- Select Language & Region.
- Under the Measurement System section, tap Measurement System.
- Choose your preferred configuration:
- Metric
- US
- UK
Once selected, a blue checkmark confirms your choice. The preference synchronises across native apps instantly without requiring a device reboot.
Customising Individual Measurement Units Separately
In addition to the global measurement profile, iOS allows you to independently override specific individual parameters, such as temperature scales, first day of the week, and number formatting styles.
Adjusting Temperature Scale (Celsius vs Fahrenheit)
If you prefer driving in miles but tracking ambient weather in Celsius, you can keep the UK or US profile while explicitly isolating the temperature unit:
- Navigate to Settings > General > Language & Region.
- Tap Temperature.
- Select either Celsius (°C) or Fahrenheit (°F).
This setting directly dictates how the stock Weather widget, Lock Screen complications, and Siri spoken weather forecasts convey daily temperatures.
Customising Number and Date Formats
Under the same Language & Region menu, tapping Number Format lets you dictate whether decimal separators appear as periods (e.g. 1,234.56) or commas (e.g. 1.234,56), preventing ambiguity when reviewing shared spreadsheets or financial documents.
Verifying Changes in Apple Maps and Fitness
After adjusting the system setting, open Apple Maps and search for a destination. Turn-by-turn navigation prompts and routing overviews will now display distances in your selected format (such as kilometres versus miles and feet).
Similarly, the Health and Fitness apps adjust walking distances, cycling trajectories, and weight tracking entries to mirror your chosen standard. Third-party applications developed using modern Apple Swift frameworks will immediately read the updated locale preference and adjust their user interfaces accordingly.