In short: SFP is 1G, SFP+ is 10G and SFP28 is 25G – three modules of the same size for three speeds. QSFP+ (40G) and QSFP28 (100G) are the wider "quad" versions that combine four lanes in one module. Which one you need is decided by the port of your device.
The names are confusingly similar, so this guide puts them side by side and explains what can be combined with what.
The five form factors at a glance
| Form factor | Speed | Lanes | Size | Typical use |
|---|---|---|---|---|
| SFP | 1 Gbit/s | 1 | small | access switches, routers, firewalls |
| SFP+ | 10 Gbit/s | 1 | small | uplinks, servers, storage |
| SFP28 | 25 Gbit/s | 1 | small | server connections in data centers |
| QSFP+ | 40 Gbit/s | 4 × 10G | wide | aggregation, older spine links |
| QSFP28 | 100 Gbit/s | 4 × 25G | wide | spine, core and data center interconnect |
SFP – the 1G workhorse
The SFP is the original small pluggable module. It runs at 1 Gbit/s and is still everywhere: in access switches, routers, firewalls and in industrial equipment. Typical types are SX for multimode fiber, LX for 10 km single-mode links and T for copper. More in our guide to 1G SFP types.
SFP+ – the same size, ten times faster
SFP+ looks almost identical to an SFP but runs at 10 Gbit/s. It is the most common module for switch uplinks and server connections. Most SFP+ ports also accept a 1G SFP, which is handy when one side of a link is older equipment – but check your device, as not every port supports the lower speed. The 10G types are explained in SR vs LR vs ER vs ZR.
SFP28 – 25G in the same slot
SFP28 keeps the size again but runs at 25 Gbit/s. It became the standard server connection in modern data centers, because it gives 2.5 times the bandwidth of 10G over the same type of cabling. Many SFP28 ports can also run SFP+ modules at 10G, which makes migration easier. Read more in what is 25G Ethernet.
QSFP+ and QSFP28 – four lanes in one module
The "Q" stands for quad: these modules are wider and combine four lanes. QSFP+ bundles four 10G lanes into 40 Gbit/s, QSFP28 bundles four 25G lanes into 100 Gbit/s. They are used where a lot of traffic comes together – between switches in the data center, in the core of a network and between sites.
Some QSFP+ modules and cables can also be split into four separate 10G links ("breakout"), so one 40G port can feed four 10G devices. Which 100G type fits which job is explained in 100G QSFP28 types.
What about XFP?
XFP is an older 10G module, larger than SFP+. You will find it in equipment that was built before SFP+ became common. If your device has XFP ports, you need XFP modules – SFP+ modules do not fit.
What can be combined?
- Same family, lower speed: SFP+ ports often accept 1G SFPs, SFP28 ports often accept 10G SFP+, QSFP28 ports often accept 40G QSFP+. Always confirm it in the documentation of your device.
- Both ends must match: a link only works when both modules run at the same speed, on the same fiber type and wavelength.
- Coding matters: whatever the form factor, many devices only accept modules coded for their brand – see our SFP compatibility guide.
Frequently asked questions
Is SFP+ backward compatible with SFP?
Usually yes: most SFP+ ports can run a 1G SFP module. The opposite does not work – an SFP+ module will not run at 10G in a 1G SFP port.
Can I put an SFP28 module in an SFP+ port?
Some SFP28 modules can run at 10G, but most are made for 25G only. If your port is SFP+, choose an SFP+ module.
What is the difference between QSFP+ and QSFP28?
They have the same size, but QSFP+ runs at 40 Gbit/s (4 × 10G) and QSFP28 at 100 Gbit/s (4 × 25G).
