All smartphones (and feature phones and other types of mobile phones) require a SIM card to connect to a mobile network – as, in fact, do mobile broadband devices, and any tablets that offer mobile connectivity.
But while you’re sure to have at least one gadget in your life that needs a SIM card, not all SIM cards are the same, as they come in three different sizes and four different common types.
Below then we’ll explain what those three different sizes are, which you’re most likely to need, how to adapt a SIM card to a different size, whether you need a new SIM card for 5G, what an eSIM is, and generally tell you everything else you need to know about SIM cards.
There are different-sized SIM cards because it has become increasingly desirable to have smaller SIM cards, since that frees up more space in a phone (or other device) for other tech, without making the phone larger.
However, while that means that the most common SIM cards are a lot smaller than a standard SIM card, the older, larger SIM card sizes are still in use too in some older devices, and in some devices that don’t need to make the most of their space.
There are five common SIM card types, which are as follows:
Nano SIM
A nano SIM is the smallest removable SIM card size, and it’s also the most modern (other than eSIMs, which we’ll get to further down) having been introduced in 2012. This is basically just a small integrated circuit with almost nothing around it, and it’s the kind used by the vast majority of modern devices.
Micro SIM
A micro SIM card is the middle size. These have more plastic around them than a nano SIM, but less than a standard SIM. They also have a slightly larger chip. In terms of smartphones, you might need one of these if your phone is over eight years old, but they’re rarely used in recent years. Indeed, they were introduced in 2003, so they’re getting on a bit now.
Standard SIM
A standard SIM is the biggest SIM card size currently in use, and despite being thought of as the ‘standard’ it’s the most rarely used. It has a large amount of plastic around the chip, and tends to only be found in the oldest of phones (and some other devices).
It was introduced back in 1996, and as the oldest of them it was the standard for a while – hence the name.
Note that standard SIM cards are also sometimes known as regular SIMs or mini SIMs – the latter because there was an even bigger credit card-sized SIM card available when these launched, but they’re no longer used.
Combi SIM
A combi SIM (sometimes called a multi SIM or trio SIM) combines all three sizes of SIM card into one, so you can easily just pop out the one you need.
This is the type you’ll typically be sent by a mobile network, so you don’t need to worry about requesting the right SIM card size. Note however that while you’ll be able to pop out whichever size you want, you won’t then be able to make the SIM card bigger again, so if you ever need to move up a size, you’ll either need an adapter (explained below) or to request a new SIM card.
eSIM
An eSIM is an embedded SIM card (that’s what the ‘e’ is for) meaning that you can’t remove it from your phone or other device. This is the newest type of SIM and it’s found in quite a lot of modern handsets, such as the iPhone 16 range – along with many other iPhones – and the Samsung Galaxy S24 range, among many other Samsung phones.
These are actually even smaller than nano SIMs, therefore freeing up more space for other tech. That small size means eSIMs are also used in wearables such as Apple Watches and Samsung Galaxy Watches.
But the main advantages of eSIMs include making it theoretically much easier to change networks and plans – since you can’t change the eSIM in your device, it needs to be possible to change network while keeping the same card, so there’s no need to swap to a new one.
Plus, multiple networks and numbers can potentially be stored on an eSIM, so you can theoretically have multiple numbers on a single SIM. And you won’t need to worry about navigating all the different SIM card sizes detailed above.
While many phones use these, at the time of writing it’s always in addition to a removable SIM card slot (at least for phones sold in the UK), so you never have to use an eSIM on a smartphone. Not all networks currently support them either, but it’s expected that these will become the standard SIM type eventually.
The chart below provides a clearer look at the exact size of each SIM card type. You’ll note that combi SIMs aren’t included and that’s because at their full size they’re the same size as a standard SIM, then if you pop out a smaller section it will match the relevant SIM card size below.
| SIM Type | Height (mm) | Width (mm) | Thickness (mm) |
|---|---|---|---|
| Standard SIM | 25.00 | 15.00 | 0.76 |
| Micro SIM | 15.00 | 12.00 | 0.76 |
| Nano SIM | 12.30 | 8.80 | 0.67 |
| eSIM | 6.00 | 5.00 | 0.67 |
Comparison of SIM card dimensions. Please note: nano SIMs and eSIMs are 0.09mm thinner than Standard SIMs and Micro SIMs.
No other differences exist between these SIM card types, it’s literally just the size. If there were other differences, then combi SIMs wouldn’t really be possible. An eSIM meanwhile is quite different, as detailed above.
Which SIM card you have will depend on a number of things. If you received one recently it’s likely a combi SIM, since that’s what networks tend to supply.
Failing that, unless it’s one that you’ve had for many years it’s probably a nano SIM, since they’ve been the most common for 8+ years.
However, to tell for sure just look at the picture near the top of this article and compare the SIM card types to yours – remembering that a mini SIM is another name for a standard SIM, and that an eSIM is embedded into the phone.
As for which you need, that will depend on your device, but the same general logic applies – for most modern smartphones, you’ll want a nano SIM. However, since networks supply combi SIMs you shouldn’t need to specify – just order one of those and then when it arrives you can pop out the right size for your phone.
The exception is if you want to use an eSIM, in which case you will usually need to request one – though many networks don’t support them.
If you have the wrong SIM card size for your phone, then wherever possible the best thing to do is simply to request a new one from your network and get your number transferred to that.
However, there are alternative options. If your SIM card is too large for your phone, then you can buy a SIM card cutting tool. These tend to look a bit like a stapler, but they trim your card down to the correct size and shape.
If on the other hand your SIM card is too small for your phone, then you can get a SIM adapter. This is a plastic frame that you can put your SIM card in, to essentially upsize it to micro or standard size.
Both of these tools can be purchased, and some independent phone accessory stores and the like also offer SIM card cutting services. However, there’s always a risk of damaging the card when cutting it, so we don’t recommend it.
Of course, none of these solutions apply to eSIMs either – an eSIM only comes in one size, but if you want to switch to or from an eSIM then you’ll have to contact your network.
In most cases you won’t need a new SIM card to access 5G – if you have a 5G plan and a 5G phone, then your current SIM card should connect to 5G networks just fine. Your network may send a software update to your SIM card when it detects that you’re trying to connect to 5G, but that’s all.
Having said that, O2 claims at the time of writing that you will need a new 5G SIM card on its network. This won’t be true in all cases as it now typically provides 5G SIM cards, but if for example you bought a 5G phone from the network before October 17th 2019, then you’ll need to switch to a new 5G card.
O2 seems to be an outlier though, as Three, EE and Vodafone all claim that your current SIM card will work for 5G. MVNOs such as Tesco Mobile also claim that you won’t need to switch SIM card, though some others don’t specify one way or the other at the time of writing. So if in doubt, check with your network.
While we’re on the subject, it’s worth noting that you’ll still be able to connect to 4G and 3G networks with a 5G SIM card/plan, so you won’t lose access to the older technologies by upgrading to the newer ones.
The different removable SIM card sizes include nano SIM (which is the smallest), micro SIM (which is the middle size), and a standard SIM or regular SIM (sometimes called a mini SIM), which is the largest. There are also eSIMs, which are even smaller than nano SIMs, but they’re built into the phone, so you won’t see them.
Mobile networks supply something called a combi SIM, trio SIM or multi SIM, which includes all three possible removable SIM card sizes. This is usually offered as standard.
No, you need the right size SIM card, which in most cases will be a nano SIM. If your device is locked to a specific network, then you also need the SIM card to be for that network – or to unlock your device.
All mobile phones use SIM cards but they don’t all use the same size ones, so you’ll need one that’s the right size for your phone. In most cases this will be a nano SIM.
Most smartphones made from around 2015 onwards will use a nano SIM card. That includes big name handsets like the iPhone 16 range, iPhone 15 range, iPhone SE (2022), Samsung Galaxy S24 range, Samsung Galaxy S23 range, and many, many more.
Nano SIM cards are the most common size – most smartphones made from around 2015 onwards use a nano SIM card.
Yes, you can use a SIM card cutting tool to convert a standard SIM to a nano SIM. However, this isn’t recommended as it risks damaging the SIM card. In general you’re better off requesting a new SIM card from your network.
A mini SIM card is another name for a standard SIM. It was originally called a mini SIM because when it first launched there was a larger full-size SIM card in use too, but these larger ones are no longer used, so mini SIMs have become standard SIMs.
A SIM card adapter is a piece of plastic that you can place a micro or nano SIM card into to convert it into a larger size.
If you put your SIM card in another phone then – as long as the card and phone support the same network – people will then be able to call and text you on that phone, and you’ll be able to make calls and send texts of your own from it, using the same network and allowances as you had on your old phone.
Phone numbers and other data may also be transferred along with the SIM card, if they were saved to the card.
A combi SIM is a SIM card that contains all three possible removable card sizes, with perforations allowing you to pop out the size you need. These are sometimes called trio SIMs or multi SIMs.
SIM cards all contain the same tech; however they vary in size, and are typically locked to a specific network.
In most cases you won’t need a new SIM card – your old one should work fine. However, on some networks (such as O2) a switch may be required. If in doubt, check with your network.
Yes. A 5G SIM card can still connect to 4G, 3G, and 2G networks. In fact, most 4G SIM cards already support 5G, so a ‘5G SIM card’ isn’t really a different thing.
