How much data do I need for a trip?

The question is nearly always asked in the wrong unit. People want a number of gigabytes and the honest answer is that there is not one, because two travellers with identical itineraries can differ by five times depending on whether they watch video.

So the useful version of the question is what you do in a day, and then how many days.

Video is the whole argument

That chart is the most useful four numbers in this guide. The same hour of television costs 0.3 GB or 7 GB depending only on the quality setting, which is a factor of more than twenty.

It explains why advice about data is so contradictory. Someone who watches nothing on their phone genuinely needs less than a gigabyte for a week away. Someone who streams an hour of ultra high definition television every evening needs fifty, and the difference between them is not their destination or their browsing, it is one habit.

The good news is that the habit is adjustable. Every streaming app has a quality setting for mobile data, and turning it down is a single tap that reduces consumption by most of its total.

Everything else is small

Once video is set aside, the numbers are reassuringly modest.

Text messages and email without attachments are close to free. A web page is a few hundred kilobytes. Maps use very little once the route is calculated, because most of the work is done on the phone. Music is middling, and a reasonable estimate for an hour at normal quality is about 40 MB.

Photographs are the other item that surprises people. A modern phone photograph is two to five megabytes, so a hundred uploads is a few hundred megabytes, which is a rounding error next to an hour of video. Video clips are the exception, and a single minute of phone footage can be a hundred megabytes.

Put together, a normal day of maps, messages, browsing and a handful of photos is well under half a gigabyte. A week of that is two or three gigabytes.

Working out your own number

The calculator below uses your own day rather than an average. Set the hours you honestly expect, and it totals them for the length of the trip.

Two notes on reading the result. It is an estimate built from typical rates, so treat it as a shape rather than a promise. And it counts only mobile data, so anything you do on hotel wifi is free of charge and free of the total.

The habit that makes a small plan enough

The pattern that gets most people through a trip on less data than they expected is simple: move the big items to wifi.

Download the maps at home. Download the episodes at home. Let the photo library back up in the evening on the hotel network rather than during the day on mobile data. Turn off automatic app updates over mobile data, since that is the quiet consumer nobody watches.

None of that is a sacrifice. It moves the traffic to a network that costs nothing and is usually faster, and it leaves the mobile plan for the things that genuinely need to happen now.

Small plan or large plan

Two schools of thought, and both have merit.

Buying small and topping up suits a trip where you are unsure. You pay for what you use and you add more when you need it, and the risk is that topping up is sometimes awkward, particularly on a travel eSIM where it means another purchase rather than a text message to your operator.

Buying large and relaxing suits a trip where the cost of running out is high, such as a drive through a remote area or a few days working from a hotel room. The risk is spending money on data that expires unused, which is the more common outcome of the two.

The middle path, and the one that usually costs the least, is to buy a modest plan and change one habit. Turning video down to standard definition or lower is worth more than doubling the size of the plan, and it costs nothing at all.

What to do if you run out

Running out is not a disaster, and knowing the options in advance removes the panic.

On a travel eSIM, the usual answer is to buy another plan and install it, which takes a few minutes and works perfectly well. On a local SIM, a top-up voucher from any shop solves it in two minutes. On hotel wifi, most things can wait until the evening.

The moment to avoid is discovering the problem at the point where you need the connection, which is exactly why the half way check is worth doing. Look at the phone’s data use against the days left, and you will never be surprised by the answer.

One last piece of arithmetic worth doing before you buy. Check what your phone has used in a normal week at home, in the settings under mobile data, and look at what consumed it. That number is a better guide to your own habits than any table, and it takes thirty seconds to find.