Quick definition: SIM form factors are the standardized sizes subscriber identity modules (SIMs) are manufactured in. There are five SIM form factors: 1FF, 2FF, 3FF, 4FF, and MFF2. Each generation of SIM is smaller than the last.

The capabilities of each form factor are the same, but they each have different dimensions, which makes them more suitable for specific kinds of devices. 2FF, 3FF, and 4FF SIMs have to be inserted into a device, while MFF2 SIMs have to be embedded—which is why they’re also called eSIMs. (1FF SIMs are no longer in use.).

If you’re building a device that relies on cellular connectivity, you need to understand the various SIM form factors available, so you can make the best choice and design accordingly. We’re going to get into the specs and compare the various form factors, but first, let’s look at why businesses use SIMs in the first place.

The advantage of SIMs

As a business, you have a range of technologies and protocols to choose from to enable machine-to-machine connectivity. Which one you use greatly depends on the use case. For example, smart home connectivity is mostly provided via Bluetooth variants, while logistics and transportation utilize cellular M2M connectivity.

Global coverage

For large-scale, global deployments, cellular M2M connectivity is generally considered the most reliable and beneficial connectivity method. You don’t need to build new infrastructure for every new deployment—you just have to connect to a network that’s already in place. As you deploy in new countries, your cellular provider may have roaming agreements with another carrier that covers that region. If not, you can select a new carrier with local coverage. 

Cellular is a WAN (wide area network) with the long-range ability to connect globally using radio waves that are sent and received via cell towers. In comparison, WiFi connectivity requires your device to remain much closer to the access point/router, preventing long-range mobility. Similarly, Bluetooth connectivity is also short range, requiring your device to be within 10–100 meters of the access point, depending on the power-class.

Built-in authentication

Cellular networks use SIM cards to authenticate devices, associate them with a legitimate subscriber, and provide secure connectivity. Hackers can spoof IP addresses, but they can’t spoof a subscriber’s identity, which is stored on a SIM card.

Secure connectivity

When your device connects to a customer’s WiFi, it shares the connection with all the other devices on the WiFi network. If these devices have a security issue, it puts your devices at risk—and the inverse is true, too. Connecting to a cellular network keeps your devices separate from your customers’ other Internet-connected devices. Manufacturers need to take IoT security seriously, and cellular connectivity gives you a number of security advantages, starting with the network your devices connect to.

If cellular connectivity is the right choice for your business, the next question is: what SIM card is best suited to my business needs? Let’s take a look at some of the design options and what you should consider when choosing a form factor.

Which SIM form factor is best for your business?

SIM cards come in four standard sizes or forms, ranging from 1FF, the first and largest SIM to be developed, to 4FF or nano-SIM, the latest and smallest in SIM design technology. (The 1FF isn’t used in modern SIM applications.) There is also an embedded SIM option—the MFF2.  

Each generation of SIM has been smaller than the last. While they’re usually referred to by the generation they come from (1, 2, 3, 4), later SIMs are also called “mini SIMs” (2FF), “micro SIMs” (3FF), “nano SIMs” (4FF), and “eSIMs” or “embedded SIMs” (MFF2). 

Note: MFF2 stands for machine-to-machine form factor.

Here are the dimensions of each form factor:

1FF: 85.6mm × 53.98mm × 0.76 mm
2FF (Mini): 25mm x 15mm x 0.76mm
3FF (Micro): 15mm x 12mm x 0.76mm
4FF (Nano): 12.3mm × 8.8mm × 0.67mm
MFF2 (eSIM): 5mm x 6 mm x 1mm

Let’s take a closer look at the SIM form factors that are currently in use today.

2FF, 3FF, 4FF SIMs

As you can see below, the actual module within the SIM card is identical—the packaging just gets smaller—which is why the form factor doesn’t impact a SIM’s capabilities.

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