Last verified 5 November 2026.
SIM cards come in four families: removable cards (2FF Mini-SIM, 3FF Micro-SIM and 4FF Nano-SIM), soldered chips (MFF2 and MFF4), the integrated SIM (iSIM) built into a modem chipset, and software-based approaches (SoftSIM and vSIM). For most industrial IoT products the soldered MFF2 is the standard choice. Nano-SIM remains the norm in phones and prototypes. MFF4 and iSIM are aimed at very small or power-limited designs.
The most common mistake is treating form factor as if it answered a second question. It does not. The form factor says how the SIM is packaged. Whether the device can download, switch and delete operator profiles remotely depends on a separate capability, the eUICC, which is what people mean by eSIM. This guide explains each form factor, how eSIM and iSIM relate to them, which one fits which device, and what to confirm before you commit a board design.
How do the eight SIM form factors compare?
The table is a starting point, not a specification. Dimensions come from standards and vendor documentation. Remote profile change depends on the individual part, so each row says what to verify rather than promising it.
| Form factor | Approx. size | Removable | Remote profile change | Typical fit |
|---|---|---|---|---|
| 2FF (Mini-SIM) | 25 x 15 mm | Yes | Not in practice | Legacy phones and older machine-to-machine equipment |
| 3FF (Micro-SIM) | 15 x 12 mm | Yes | Not in practice | Older smartphones and tablets |
| 4FF (Nano-SIM) | 12.3 x 8.8 mm | Yes | Only if the card is an eUICC product | Phones, prototypes, serviceable gateways |
| MFF2 | About 6 x 5 mm | No, soldered | Only if the chip is an eUICC | Industrial and long-life IoT |
| MFF4 | About 2 x 2 mm | No, soldered | Only if the chip is an eUICC | Wearables and compact sensors |
| iSIM | No separate package | No, part of the SoC | Depends on the chipset and its provisioning support | Very small, high-volume devices |
| SoftSIM | Software | Not applicable | Depends on the implementation | Operator-controlled private networks, niche IoT |
| vSIM | Software or service | Not applicable | Depends on the service | Consumer travel apps |
Package is not capability. eUICC is the technology behind remote SIM provisioning, commonly called eSIM. A form factor can carry it or not. Always ask the supplier whether a specific part number is an eUICC.
What are the removable SIM sizes?
Most people meet a removable SIM first: slide it into a tray and the phone connects. The three sizes share one electrical interface, which is why a smaller card is the same chip with less plastic around it. The sizes are defined in ETSI specifications for the UICC, including ETSI TS 102 221.
Mini-SIM (2FF) measures 25 by 15 mm and dates from the 1990s. Today it survives in legacy phones and older machine-to-machine hardware that is still in the field. Micro-SIM (3FF) measures 15 by 12 mm with the same contact layout, which let phone makers build thinner devices without changing carrier infrastructure. Nano-SIM (4FF) measures 12.3 by 8.8 mm and strips away nearly all the remaining plastic. Apple introduced it in the iPhone 5 in 2012, and it is still the standard removable size in smartphones.
For IoT, Nano-SIM has a real job in prototyping. You can move a card between devices, test different networks and iterate quickly. It was not designed for decade-long deployments in vibration, moisture or heat, which is where soldered parts take over. A useful comparison is a USB flash drive: ideal for portability, but not what you would leave permanently attached to equipment in the field.
Plan the switch early. If a pilot runs on Nano-SIM, decide before production whether the shipping product moves to MFF2 or MFF4. A new package changes the board footprint, the mechanical design and the manufacturing process, and a late change can mean a layout revision.
Why is MFF2 the industrial default?
MFF2 (Machine Form Factor 2) is an eight-pin surface-mount SIM chip of roughly 6 by 5 mm. It is soldered to the circuit board during assembly, which sounds restrictive but is an advantage in harsh conditions. With no tray or card, there is nothing to be dislodged by vibration, shock, dust or moisture. Parts qualified for extended temperature ranges exist, with some vendors rating them up to 105 degrees Celsius, but the rating belongs to each part number, so check the datasheet of the exact SKU you plan to use. The MFF2 package is defined in ETSI TS 102 671.
MFF2 turns up wherever devices are installed once and left alone: vehicle and container trackers, utility meters, and industrial sensors in remote or hazardous places. Because nobody can swap a card cheaply on a sealed meter or an outdoor asset tag, the question of how to change operator later matters more than the package itself.
Do not assume MFF2 means eSIM. An MFF2 chip can be a traditional single-operator SIM that happens to be soldered, or an eUICC that supports remote profile changes. Verify eUICC support during component selection. If you skip this check, you may discover after deployment that changing operator still needs a field visit.
Fleets of MFF2 devices across several carriers or countries still need someone to manage subscriptions, usage and profile changes. Our guide to IoT connectivity management platforms covers what that layer does, our IoT connectivity comparison sets out the connectivity options around it, and our IoT SIM cards guide covers choosing a SIM for connected devices.
Where do MFF4 and iSIM fit?
MFF4: a smaller discrete chip
MFF4 is an eight-pin soldered package of about 2 by 2 mm. It is smaller than MFF2 but is still a discrete component on the board. Arm Kigen describes MFF4 eSIMs as already designed into commercial products across industrial and consumer markets. Because the part is small, it frees board space, and designers of battery-powered devices that wake briefly to transmit often care about a smaller silicon footprint and low idle draw. Treat any power saving as something to measure on your own design rather than a given.
The reason to choose MFF4 over iSIM is supply chain control. The SIM stays a separate part that you can source and certify on its own, independently of the modem or processor vendor. Typical uses are smartwatches, medical wearables, compact trackers and e-bikes.
iSIM: the SIM inside the chip
iSIM, short for integrated SIM, puts the SIM function inside the device’s system-on-chip (SoC) or modem, so there is no separate SIM component and no extra board area. For high-volume consumer electronics and ultra-compact IoT products, many engineers see it as the long-term direction.
The trade-off is dependency. Because the SIM function belongs to the chipset, changing modem or SoC vendor later means changing the SIM approach too, and certification is generally more involved than for a separate part. On security, an integrated SIM runs in a secure area of the chip, and GSMA publishes a security evaluation approach for integrated eUICCs in SGP.18. Ask a supplier for the certification status of the exact chipset rather than relying on a general statement that iSIM is more secure.
| Feature | MFF2 | MFF4 | iSIM |
|---|---|---|---|
| Size | About 6 x 5 mm | About 2 x 2 mm | Part of the SoC |
| Board footprint | Moderate | Minimal | None |
| Separate component | Yes | Yes | No |
| Sourcing flexibility | Independent of the modem vendor | Independent of the modem vendor | Tied to the chipset |
| Certification | Certified as a standalone part | Certified as a standalone part | Usually part of the chipset program |
| Best fit | Industrial and long-life IoT | Wearables and compact devices | High-volume, ultra-compact devices |
How do eSIM, iSIM and form factor relate?
This is the most misunderstood point in the SIM world, and it causes avoidable procurement mistakes. eSIM is not a form factor. It is a capability: an eUICC (embedded Universal Integrated Circuit Card) that can have operator profiles downloaded, switched and deleted remotely, without swapping a card. Two GSMA specification families govern it: SGP.22 for consumer devices and SGP.32 for IoT devices. Our SGP.22 vs SGP.32 guide explains the difference, and the remote SIM provisioning guide covers how a profile reaches a device.
In everyday talk, people also say “eSIM” for a soldered chip such as MFF2. That is shorthand for a soldered chip that includes an eUICC, and it is the source of the confusion. The independence of the two questions works in every direction:
- A phone can run an eSIM profile and still have a removable Nano-SIM slot. The package and the capability are different decisions.
- An MFF2 chip can be soldered to a board and still be a traditional single-operator SIM.
- An MFF4 chip or an iSIM can be eUICC-capable, but you should confirm the specific part and the provisioning services behind it.
If you want a mental model, the form factor is the shape of the power socket and the eUICC is whether the socket supports smart metering. The two design choices are independent. For consumer-phone context on the capability side, see our eSIM explainer and the guide to dual SIM and eSIM.
eSIM versus iSIM at a glance
When people compare “eSIM” with “iSIM” they usually mean a separate soldered eUICC chip against an eUICC integrated into the SoC. Read in that sense, the comparison looks like this.
| Aspect | Soldered eSIM chip (MFF2 or MFF4) | iSIM |
|---|---|---|
| Where the SIM lives | Separate chip on the board | Inside the SoC or modem |
| Space | Takes board space, least with MFF4 | No separate board space |
| Remote provisioning | Yes, when the chip is an eUICC | Yes, when the chipset supports it |
| Replacing the SIM component | Possible by changing the part, subject to the board design | Not separable from the chipset |
| Certification | Standalone certification of the SIM part | Tied to the chipset and its security evaluation |
| Best fit | Industrial, wearable and compact devices | Very small, high-volume devices |
In practice the choice is rarely “eSIM or iSIM”. It is a question about the hardware architecture: does the product need a SIM component that the team sources separately, or is it built around a chipset that already includes one? Choose a separate eUICC chip for flexibility and a simpler bill-of-materials decision, and an iSIM when board space and unit economics at scale justify a deeper tie to the chipset vendor.
What are SoftSIM and vSIM?
SoftSIM stores SIM credentials in the device’s general-purpose memory instead of a dedicated secure chip. vSIM (virtual SIM) is a related term, usually a service where the profile is hosted remotely and delivered through an app, which is common in consumer travel data offers. Both remove SIM hardware from the design.
The practical limits are carrier acceptance, which is inconsistent, certification status that varies by implementation, and a security model that is weaker than hardware-rooted designs unless the implementation compensates. Neither is a mainstream production route for most IoT deployments, but SoftSIM appears in some private LTE and 5G networks where one operator controls the whole stack.
How do you choose a SIM form factor?
Answer five questions about the device. They narrow the choice quickly, and the answers also tell you what to ask your supplier.
- Is it a consumer phone or tablet? If yes, a Nano-SIM slot plus eSIM is the universal choice.
- Is physical size the main constraint? For wearables and compact trackers, look at MFF4 or iSIM.
- Will it face a harsh environment? Vibration, heat and moisture point to a soldered MFF2, and you should check the part’s environmental rating.
- Do you need to change operator remotely over several years? Then the part must be an eUICC and the provider must support remote profile changes. The package alone does not answer this.
- Are you still prototyping? Nano-SIM keeps carrier swaps simple, but plan the move to the production package early.
| Use case | Likely form factor | Why |
|---|---|---|
| Consumer smartphone | Nano-SIM plus eSIM | Universal standard, wide operator support, dual-SIM flexibility |
| Wearable or smartwatch | MFF4 or iSIM | Small board footprint and tight power budget |
| Industrial asset tracker | MFF2 | Durability and an extended temperature range, per part |
| Smart meter | MFF2 with an eUICC | Long life and remote profile changes without a site visit |
| Connected vehicle or EV charger | MFF2, automotive-qualified part | Vibration and heat tolerance; confirm qualification for the exact SKU |
| Early prototype | Nano-SIM | Easy carrier swaps during testing |
Module choice and SIM choice are linked. Modules differ in which SIM interfaces they support, so settle both together and confirm eUICC support against the module datasheet and the SIM supplier rather than a general compatibility list. For sensor-specific connectivity needs, see our guide to IoT sensors and connectivity.
Why does SGP.32 matter for form factor choice?
SGP.22 was designed for consumer devices, where a user scans a code or taps a prompt. IoT devices often have no screen, limited power and intermittent connectivity, so the GSMA wrote SGP.32 for them. It shifts more of the profile management logic to the server side, which makes remote provisioning at fleet scale practical. GSMA released the first version in 2023 and has issued revisions since, so a supplier claiming compliance should name the version and the device components that implement it.
For form factors, SGP.32 is a property of the eUICC and its software, not of the package. MFF2, MFF4 and iSIM implementations can support it, while a removable consumer eSIM generally follows SGP.22. If you plan to change operators in the field, ask each supplier which specification their part supports. Retrofitting remote provisioning after launch is far harder than choosing it at the start. The eSIM for OEMs page covers the manufacturer side of this decision.
Conclusion: decide the package and the capability separately
There are eight SIM form factors, and each has a role. Nano-SIM serves phones and prototypes, MFF2 serves industrial and long-life IoT, MFF4 and iSIM serve the smallest and most power-limited designs, and SoftSIM and vSIM remain niche. The right pick depends on device size, operating environment, expected lifetime, and whether you need remote operator changes.
Keep two checklists. For the package: size, environmental rating, soldering, sourcing and certification. For the capability: is the part an eUICC, which GSMA specification does it follow, and which provider manages the profiles. Getting both right before the board is frozen avoids a redesign later. A connectivity management layer on top, such as a platform like Spenza, then keeps provisioning, usage and carrier relationships consistent across whichever hardware your team selects.
SIM card form factor FAQs
What is the difference between MFF2 and eSIM?
MFF2 is a physical package: a small chip soldered onto the board. eSIM is a capability: an eUICC that can download, switch and delete operator profiles remotely. An MFF2 chip may or may not include that capability, so confirm eUICC support on the exact part before you order.
Is iSIM the same as eSIM?
No. iSIM describes where the SIM function lives, inside the device’s system-on-chip. eSIM describes remote profile management. An iSIM can support remote profile management, but you should confirm it for the specific chipset and the services behind it.
What is the smallest SIM form factor?
iSIM, because it has no separate package at all and is part of the SoC. Among discrete parts, MFF4 at about 2 by 2 millimeters is smaller than MFF2 at roughly 6 by 5 millimeters. Smaller is not automatically better, since certification and sourcing differ.
Which SIM form factor is best for IoT?
It depends on the device. A soldered MFF2 is the usual choice for industrial and long-life products, MFF4 or iSIM suit very small or battery-limited designs, and a removable Nano-SIM suits prototypes and serviceable gateways. Decide the form factor and the profile capability separately.
Can a Nano-SIM be an eSIM?
The card itself can be a removable eUICC product in some cases, but most phones now run eSIM from a chip inside the device alongside a physical Nano-SIM slot. The two questions, package and remote provisioning, are independent. Check the product specification rather than inferring one from the other.
What is SGP.32 and why does it matter for IoT?
SGP.32 is the GSMA specification for remote SIM provisioning on IoT devices, which often have limited interfaces and intermittent connectivity. It moves much of the profile management to a remote server side. If you want to change operators in the field, ask whether the eUICC and the provider support it.
What is the difference between SoftSIM and vSIM?
SoftSIM keeps SIM credentials in the device’s general-purpose memory instead of a dedicated secure chip. vSIM usually means a virtual SIM service, often an app or cloud-hosted profile used for consumer travel data. Carrier acceptance and certification vary, so neither is a default for production IoT.
Do I need to change my PCB to move from Nano-SIM to a soldered SIM?
Usually yes. A soldered part has a different footprint and no holder, and the mechanical and manufacturing process changes with it. Plan the switch before you finalize the board, because a late change can force a layout and certification rework.
