Fiber optic cable names look like alphabet soup: OM1, OM3, OM4, OS2. The good news is the choice usually comes down to two questions: how far does the link need to run, and what do your transceivers (SFP/SFP+/QSFP) expect? This guide walks through both so you can buy the right cable the first time.
Step 1: Multimode or single-mode?
Multimode fiber (OM1 to OM5) has a wider core (50 or 62.5 microns) and is designed for short links inside a building: server rooms, switch-to-switch runs, labs, and rack-to-rack connections. Multimode optics are inexpensive, which keeps total cost low.
Single-mode fiber (OS1/OS2) has a tiny 9-micron core and carries one mode of laser light over very long distances. Use it for campus links between buildings, metro and telecom runs, and anything beyond a few hundred meters. The cable is cheap, but the laser optics at each end cost more than multimode optics.
Important: match the cable to your transceivers. A multimode cable on single-mode optics (or the reverse) is not supported and may give no link or an unstable one. Always check what your SFP or NIC model requires.
Step 2: Pick the grade for your distance and speed
| Type | Core size | Typical jacket color | 10 Gbps reach | 40/100 Gbps reach |
|---|---|---|---|---|
| OM3 (multimode) | 50/125 µm | Aqua | Up to 300 m | Up to 100 m |
| OM4 (multimode) | 50/125 µm | Aqua or violet | Up to 400 m* | Up to 150 m |
| OS2 (single-mode) | 9/125 µm | Yellow | Up to 10 km or more (depends on optics) | Up to 10 km or more (depends on optics) |
*Standard IEEE rating for 10GBASE-SR. Some manufacturers quote longer distances; always check the specification for your exact optics. Reach figures are for standard transceivers at 850 nm (multimode) and 1310 nm (single-mode).
OM3: the practical baseline
OM3 is laser-optimized 50/125 multimode fiber and the sensible minimum for any new multimode installation. It handles 10G to 300 m and is a great fit for most server rooms, offices, and home labs.
OM4: more headroom for a small premium
OM4 uses the same 50/125 construction as OM3 but with tighter bandwidth specs, which means longer reach at high speeds (10G to 400 m, 40/100G to 150 m). If you plan to upgrade to 25G, 40G or 100G later, OM4 is usually worth the small price difference.
OS2: long distance and future-proofing
OS2 is the choice for links between buildings, across a campus, or anywhere over about 400 m. Single-mode cabling also stays useful as speeds increase, because the speed limit is set by the optics, not the cable.
What about OM1, OM2 and OM5?
- OM1 (62.5/125, orange): legacy. Reaches about 275 m at 1G but only about 33 m at 10G. Buy only to match existing OM1 cabling.
- OM2 (50/125, orange): legacy. About 550 m at 1G and about 82 m at 10G.
- OM5 (50/125, lime green): built for short-wavelength division multiplexing (SWDM). For standard 10G it performs like OM4, so it only makes sense if you use SWDM optics.
Quick buying guide
- Server room or office, 10G, under 300 m: OM3 or OM4 duplex LC-LC.
- Same rack or neighboring racks: OM4 LC-LC in 1 to 5 m lengths. Short cables keep things tidy.
- Planning a 40G/100G upgrade: OM4.
- Between buildings or over 400 m: OS2 single-mode with connectors that match your optics.
- New switch to an older patch panel: match the fiber grade already installed, then pick the connector type (see our LC vs SC vs ST connector guide).
How to tell what fiber you already have
- Check the jacket print. Most cables are labeled with the type (for example "OM3 50/125").
- Check the jacket color. Orange usually means OM1/OM2, aqua or violet means OM3/OM4, lime green means OM5, and yellow means single-mode. Color is a hint, not a guarantee.
- Check the transceiver label. SR usually means multimode (850 nm); LR/LX usually means single-mode (1310 nm).
Frequently asked questions
Can I use OM3 and OM4 together in one link?
Yes, both are 50/125 multimode, so they are physically compatible. The link's maximum distance will be limited by the lower-grade segment.
Is OM4 worth it over OM3?
For short links under 100 m at 10G, OM3 is usually enough. OM4 is worth it when you want extra distance or plan to move to 40G/100G.
Can I connect multimode and single-mode cables together?
Not recommended. The core sizes differ, so you can get heavy signal loss and unreliable links. Keep each link on one fiber type that matches the transceivers.
Do I need duplex or simplex?
Most links use duplex (two strands: transmit and receive). Simplex cables are for single-strand BiDi optics and specific equipment.
Ready to shop? Browse our fiber optic cable collection, and contact us with your transceiver model if you are not sure what to order.