How many Megabytes does an iMessage use when sent over mobile data? I’m asking because I’m on a pay as you go plan and I want to send iMessages on mobile data. I want to know how much will it cost me?
Sending an iMessage involves two things:
Sending the message payload (Text or Data in the form of audio, video or image) to the Apple's iMessage server, and
The metadata exchanged between device and Apple's iMessage server for the iMessage protocol (determining if the receiving party is registered with iMessage by contacting the Apple's servers, fetching the delivery and read status and time of iMessage etc.)
The metadata exchange takes up minuscule amount of data and the process is pretty optimised. The amount of data for audio, video and image equals the size of the asset (unless it is sent in compressed form). Emojis are sent in the form of textual code and are not treated as image. Text doesn't take up too much data.
iMessage service is provided by Apple free of cost. However, data charges for any data exchanged with the Apple servers over the Internet are applicable depending on the type and pricing of your Internet connection.
You can determine the cellular data usage on a per app basis, as outlined by Apple in the support article, Check the cellular data usage on your iPhone and iPad:
View how much data you're using
To see how much cellular data that you've used, go to Settings, then tap Cellular or Mobile Data. If you're using an iPad, you might see Settings > Cellular Data instead.
To see how much cellular data an app is using, scroll down to find the app. If you don't want an app to use cellular data, you can turn it off for that app. When cellular data is off, apps use Wi-Fi for data.
To see the cellular data usage for individual System Services, go to Settings, then tap Cellular or Mobile Data. Then scroll to the bottom of the screen and tap System Services. Cellular data can't be turned on or off for individual System Services.
Depending on your carrier, you may see overall cellular data usage displayed on this screen. If you don’t have this option, or have questions about your data usage, contact your carrier.
Since, the mobile data service cost vary across providers, you can use the guidelines mentioned above to get an idea about how much will it cost to send an iMessage.
Thus, the simple answer is:
Total cost = ( Total number of bytes transmitted + received in sending an iMessage ) multiplied by ( Mobile data cost per byte ).
i.e. once you have determined the total data exchanged (sent + received) in sending an iMessage, you can get a precise idea about how much it will cost to send that iMessage over mobile data.
To answer your question as best as possible, lets look at the major points of where the data fluctuates. You didn't say if you had an SMS (Texting) plan with your carrier either, so if you do, just use that.
Media messages with pictures/video will be considerably higher than a basic message.
A basic message is kilobytes in size and very small.
iMessage was developed as a free messaging service between Apple devices via Wifi networks which wouldn't count toward you texts per month/data plan.
So the answer to how much it will cost you is not available from the AskDifferent community without knowing how much you'll be using it and what for.