iPhone with a SIM card and SIM card holder next to it

What SIM card do I need for my phone?

With technology advancing, mobile phones have become smaller, slimmer and sleeker (some even fold now!).

As phone sizes change, their hardware must adapt as well. This has led to smaller and smaller SIM cards being created to fit inside.

In the UK at the moment, we have three different SIM card sizes depending on which handset you have. Discover what size SIM your phone needs in this guide!

What is a SIM card?

A “Subscriber Identity Module” or SIM card allows you to connect to a phone network, so you can make and receive calls, send text messages, and use mobile data.

These tiny cards hold a lot of information about your phone, including its number and network provider. The unique identification number on every SIM associates your number, minutes and other account details with device usage, so you always know where you’re at use-wise.

No matter what phone you have, everyone needs a SIM card for theirs to function properly.


What are the different SIM card sizes?

There are three different SIM card sizes currently available to UK mobile customers - Standard, Micro and Nano

SIM card












Standard SIM card

This is the biggest of the three SIM sizes, at 25mm x 15mm. It’s not as commonly used anymore, but remains the most compatible choice for older handsets or less high-tech models with more space inside for hardware.

Micro SIM card

The Micro SIM card is smaller than the standard, measuring 15mm x 12mm. First introduced in 2003, it became more widely used after being built into the iPhone4. However, like the standard SIM, it’s becoming increasingly obsolete as manufacturers favour the even smaller nano SIM.

Nano SIM card

Currently the smallest (and most common) SIM card on the market, the nano SIM measures approximately 12.33mm x 8.8mm! Launched in 2012, it's the most commonly used SIM type in smartphone releases. With hardly any plastic border around the chip itself, it will be interesting to see if SIM cards get any smaller than this!


Where is the SIM card slot located?

If you’re switching SIMs, you’ll have to take the old one out and replace it with the new one. This means finding and popping open your phone’s SIM card slot.

The SIM card slot is usually in one of three places: 

1. Exterior on the side

Sometimes you can only access your SIM card through the phone’s interior (see points 2 and 3), but on many iPhones and Androids, the slot is on the exterior.

Turn your phone on its side and you should be able to see a cover with a little pinhole beside it. You can then use the SIM extractor tool (usually supplied with your new card) to push open the card tray.

2. Under the back cover

If the back cover on your phone is removable, your SIM card slot may lie underneath; simply lift it off to find out.

3. Under the battery

If your battery is removable, then the SIM card tray may be located under this.


Can you change your SIM card size?

Most modern SIMs come with an adaptor that lets you choose whatever size you need - just pop the SIM card out and you’re ready to go!

If you’ve kept this adaptor, you can easily swap SIM cards. The chip part should fit neatly inside the plastic frame and become either a nano, micro or standard size, depending on your need.

If you’ve lost the adaptor, don’t panic - you can easily buy a replacement online.

Can you convert a standard SIM to a nano SIM?

This is a little trickier. If you’re using an old, fixed-size SIM card, you’ll need to somehow make it smaller.

The best thing to do is contact your network, who should be able to send you a replacement SIM card.


Which SIM card does my phone need?

If you’ve switched networks or just bought a new phone, you’ll need to perform a SIM swap. That’s all well and good, but you may not know what size card you need!

As we’ve explained, most smartphones take a nano SIM, while older models are more compatible with standard or micro cards. You must do plenty of research into your chosen device and manufacturer to find out which SIM size they require.

Alternatively, a quick browse through your mobile’s setup manual (if you have this) should tell you what size SIM card it takes.

And with Asda mobile, when you order your SIM, we actually send all three sizes - so you’re guaranteed to get the card you need!


How to change your SIM card

After locating the SIM card slot, all you need to do is take the old SIM out and replace it with the new one.

The old SIM is effectively useless now, unless of course you’ve swapped networks. As a security precaution, keep it somewhere safe or destroy it; remember, it still has all your personal data stored!

When inserting your new SIM card, there’s a 45-degree notch in one corner that aligns with the tray, so you’ll know which way to insert it. Once inserted, simply close the tray and place the cover back on your phone (if that’s how it was accessed).

If you need help swapping SIM cards, watch our step-by-step video guide:


Find SIM only deals with Asda mobile

Starting your SIM only journey with Asda mobile is quick and simple. Check out our SIM only deals to find a bundle that best suits you!

Moving to our network from a different provider? You’ll need a PUK code to keep your old number.


Discover more about SIM only

If you’re not sure whether SIM only is right for you, check out our blogs on all the advantages and benefits of switching to this type of phone plan:

Also, follow Asda mobile on Facebook and Twitter to get updated about our latest guides.

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