Apple understands that some iPhone and iPad users may prefer to keep tabs on their cellular network data usage, especially if they risk incurring charges by going over a certain limit.

The same goes for users who have a bandwidth cap on their broadband network, or anyone who regularly connects to a public Wi-Fi network that charges per megabyte.

That's why in iOS 13, Apple has included a Low Data Mode for apps that use cellular and Wi-Fi connections. The feature sends an explicit signal to apps to reduce their network data use by deferring non-compulsory tasks and disabling background app refresh.

To turn on the cellular or Wi-Fi setting on your iPhone or ‌iPad‌, simply follow these steps.

How to Turn On Cellular Low Data Mode

1. Launch the Settings app on your device
2. Tap Cellular (or Mobile Data, depending on your region).
   
   
3. Tap Cellular Data Options (or Mobile Data Options).
4. Tap the Low Data Mode switch to toggle it to the green ON position.

How to Turn On Wi-Fi Low Data Mode

1. Launch the Settings app on your device
2. Tap Wi-Fi.
3. Tap the info button (an encircled 'i' icon) alongside the Wi-Fi network in question.
   
   
4. Tap the Low Data Mode switch to toggle it to the green ON position.

Note that a given third-party app must explicitly support Low Data Mode for there to be any change in its data usage, otherwise enabling the mode won't have any effect.