How much mobile data ChatGPT uses abroad, and how to measure it

Why there is no official megabyte figure

OpenAI's help centre has detailed pages on ChatGPT Voice, on uploading files, on searching the web and on creating images. They cover plans, usage limits, file sizes and settings, but none of them gives a figure per message, per minute or per image. The numbers that circulate online are estimates by third parties, and this article does not repeat them.

A single figure would not help much anyway. The same app can send a two-line question or a photo of up to 20 MB, which is OpenAI's limit per image; it can return a short answer or hold a voice conversation for half an hour. Some of the work happens on OpenAI's side and some streams to your phone. What you spend depends on which of those you do, and your phone can tell you exactly.

What each feature actually moves

• Text chat: your message goes up and the answer comes down as text. Long answers, tables and code are still text, so this is the light end of ChatGPT.
• Voice: OpenAI offers Live, Advanced and Standard under Settings, Voice. Live listens and speaks at the same time, so audio flows both ways while the call is open; Standard transcribes what you say before it answers.
• Video and screen sharing: available in Advanced voice in the iOS and Android apps for eligible subscribers. They add a live camera or screen feed on top of the audio, so test them before counting on them over mobile data.
• Photos and files: the whole file is uploaded. OpenAI's limits are 20 MB per image and 512 MB per document or audio file, and video files can be attached too.
• Generated images: they are created on OpenAI's side, which can take a few minutes, and your phone receives the finished image. Every edit or new version is another image, and all of them are saved under Images in the app.
• Web search: ChatGPT sends the queries to search providers itself and returns an answer with citations, sometimes with images or, on iOS and Android, a map. Tapping a citation opens the full web page, which costs what it would in any browser.

If you only want to ask out loud, Dictation is the lighter route. OpenAI describes it as recording a prompt that you review and then send as text, so the phone records while you speak the question, not for the length of a conversation.

The ten-minute test on an iPhone

Apple's iPhone guide shows data per app under Settings, Cellular: scroll down to the list of apps and tap Show All, and the cellular data used appears under each one. System Services have their own entry above the list, and at the very bottom there is Reset Statistics.

To measure, take a screenshot of the list if you want to keep your totals, tap Reset Statistics, turn Wi-Fi off and do one thing in ChatGPT for ten minutes: a voice conversation, for instance, or a run of text questions. Then go back to Settings, Cellular and read the figure under ChatGPT. Divide it by ten for a per-minute rate, then multiply by the minutes you expect to use it each day and by the days of the trip.

Repeat with the other things you plan to do, one at a time: sending three photos, generating two images, a session with search. The method is the same for Gemini, Copilot or any other assistant, since each app has its own line. With Dual SIM, Apple says the figures are for the number selected for cellular data, and it adds that your carrier has the most accurate count for a billing period; the phone's counter is for comparing features.

The same test on Android

On a Pixel, Google's path is Settings, Network and internet, SIMs, then App data usage, where you choose the period with the arrow and see how much each app used below the graph. On a Samsung Galaxy, Samsung puts the list in Settings, Connections, Data usage, Mobile data usage.

Neither help page describes a reset for one app, so work by subtraction: note ChatGPT's figure for the current period, run your ten minutes with Wi-Fi off and read it again. The difference is your test. Google points out that the phone measures this itself and that carriers may count differently, which matters for a bill but not for comparing one feature with another.

While you are on that screen, a Pixel can also warn you. Under Data warning and limit you set an amount, and you get a notification when usage reaches it. On a trip it is a cheap early alarm, and Samsung has the same idea under Billing cycle and data warning.

Keeping ChatGPT on Wi-Fi only

• iPhone: Settings, Cellular, then turn ChatGPT off in the list of apps. Apple says the iPhone then uses only Wi-Fi for it, so it works at the hotel and stays quiet in the street.
• iPhone, a softer option: Low Data Mode, in Settings, Cellular, Cellular Data Options, Data Mode. Apple says it pauses automatic updates and background tasks when the iPhone is not on Wi-Fi.
• Pixel: Data Saver, in Settings, Network and internet. Google says most apps then get background data only over Wi-Fi, while an app you are actively using can still use mobile data.
• Samsung: Settings, Apps, ChatGPT, Mobile data, then turn off the switch that allows background data. Samsung warns that some app features may stop working while the app is closed.

Two leaks are easy to miss. A voice conversation can carry on while you use other apps or lock the phone; OpenAI says it only ends when you end it, force close the app, or reach a usage limit or the maximum session length, so hang up when you are done. On an iPhone, Connectivity Assist, at the bottom of Settings, Wi-Fi, uses cellular data when Wi-Fi is slow or unusable. Apple warns it can mean more cellular data and says it is not used while roaming internationally or in Low Data Mode; if you want to be sure, switch it off. The trade-offs are in hotel Wi-Fi vs mobile data.

With no signal at all

ChatGPT needs a connection. OpenAI's troubleshooting page reads its network errors as the device being unable to reach its servers, so on a plane, in a metro tunnel or in a valley without coverage, it simply stops answering.

For the jobs travellers most often give an assistant, there are offline tools. Google Translate lets you download languages and translate without an internet connection, and Google suggests connecting to Wi-Fi first. Apple's Translate app does the same from Settings, Apps, Translate, Languages, and setting On-Device Translation to Always keeps every translation on the iPhone. Maps can come with you too, as in using Google Maps offline.

The other habit is to ask the big questions on Wi-Fi. Plan the route, the opening hours and the phrases you need over breakfast, then save the answer in Notes or as a screenshot so you can read it without signal.

Local answers and a travel eSIM

When you ask for restaurants or the weather nearby, OpenAI says ChatGPT may use an approximate location based on your IP address, that sharing your device's location is optional and off by default, and that a VPN or the network's location can throw that estimate off. If the results point at the wrong city, put the city or neighbourhood in the question, or turn on location in Settings, Data controls, Location.

For everything else, ChatGPT treats a travel eSIM like any other connection. A Snoozim eSIM is data-only, arrives as a QR code by email and starts counting when it first connects at your destination; if you use ChatGPT on a laptop through the phone's hotspot, that traffic comes out of the same data. Add what your tests showed to the data calculator or to how much data do I need, and if you run short, top-ups go onto the same eSIM, as explained in how to top up a travel eSIM.