Single-mode vs multimode fiber: differences, reach and cost
Single-mode (OS2) and multimode (OM1–OM5) fiber compared: core size, light source, reach at 1G to 400G, jacket colours, what each costs and which to choose for FTTH, campus and data centre links.
What is the difference?
Both fibers have the same 125 µm glass cladding. The difference is the core that carries the light, and the light source each one is built for.
| Single-mode (OS1, OS2) | Multimode (OM1–OM5) | |
|---|---|---|
| Core | About 9 µm (mode-field diameter 9.2 µm at 1310 nm for G.652.D) | 50 µm (OM2–OM5) or 62.5 µm (OM1) |
| Light paths | One | Many |
| Light source | Lasers at 1310 and 1550 nm | 850 nm VCSELs (OM5 also 850–953 nm) |
| Attenuation (typical fiber) | ≤ 0.34 dB/km at 1310 nm, ≤ 0.21 dB/km at 1550 nm | About 2.3–3.0 dB/km at 850 nm |
| Reach at 10G | 10 km (LR), 40 km (ER), 80 km (ZR) | 300 m on OM3, 400 m on OM4 |
| Jacket colour (TIA-598) | Yellow | Aqua (OM3, OM4), lime green (OM5), orange (OM1, OM2) |
| Typical use | FTTH, access, metro, campus backbones, long data centre links | Short links in buildings and data centres |
Single-mode fiber lets only one path of light through its narrow core. Without paths of different lengths, a pulse does not smear out, so the reach is limited by loss and by the optics, not by the fiber’s bandwidth. Multimode fiber lets many paths through its wide core. The paths arrive at slightly different times (modal dispersion), and the faster the signal, the shorter the distance before the pulses blur together. That is why multimode reach falls from 550 m at 1G to about 100 m at 100G.
Multimode grades: OM1 to OM5
| Grade | Core | Modal bandwidth at 850 nm | Jacket | Status |
|---|---|---|---|---|
| OM1 | 62.5 µm | 200 MHz·km | Orange | Legacy; avoid for new work |
| OM2 | 50 µm | 500 MHz·km | Orange | Legacy 1G links |
| OM3 | 50 µm, laser-optimised | 2,000 MHz·km | Aqua | 10G to 300 m, 100G to 70 m |
| OM4 | 50 µm, laser-optimised | 4,700 MHz·km | Aqua (violet in some European markets) | The usual choice for new multimode cabling |
| OM5 | 50 µm, wideband | 4,700 MHz·km, specified 850–953 nm | Lime green | Short-wave WDM optics; same reach as OM4 for ordinary SR optics |
Bandwidths are the minimums in IEC 60793-2-10: effective modal bandwidth for OM3 to OM5, overfilled-launch bandwidth for OM1 and OM2. Our fiber optic color code tool shows the jacket, tube and fiber colours side by side.
How far each fiber reaches, by speed
| Ethernet application | OM1 | OM2 | OM3 | OM4 | Single-mode |
|---|---|---|---|---|---|
| 1G (1000BASE-SX / LX) | 275 m | 550 m | 550 m | 550 m | 5 km (LX), 10 km (LX10) |
| 10G (10GBASE-SR / LR) | 33 m | 82 m | 300 m | 400 m | 10 km (LR), 40 km (ER) |
| 25G (25GBASE-SR / LR) | — | — | 70 m | 100 m | 10 km |
| 40G (40GBASE-SR4 / LR4) | — | — | 100 m | 150 m | 10 km |
| 100G (100GBASE-SR4 / LR4) | — | — | 70 m | 100 m | 10 km (LR4), 40 km (ER4) |
| 400G (400GBASE-SR8 / DR4 / FR4) | — | — | 70 m | 100 m | 500 m (DR4), 2 km (FR4), 6 km (LR4-6) |
Reaches are IEEE 802.3 values, except 40 km for 10G ER, the engineered-link reach ER modules are sold for; multimode figures at 1G are minimums, and many installations go further. Parallel multimode optics (SR4, SR8) need 8 or 16 fibers on MPO connectors; see our guide on MPO polarity. Long single-mode links still need a loss budget: the fiber loss calculator adds fiber, connectors and splices for you.
What each costs
The cable and the optics pull in opposite directions.
- Cable. Per metre, OM3 and OM4 cable cost more than single-mode cable with the same fiber count, because laser-optimised multimode fiber is harder to make than G.652.D. For budgeting, bare G.652.D fiber sold for about $12–15 per fiber-km in China in August–September 2026 (our October 2026 price guide).
- Optics. Multimode systems save money in the transceivers: 850 nm VCSEL optics cost less than the lasers single-mode needs, and the gap is largest at long reach and high speed. Compatible 10G SFP+ LR modules list at about $14–18 and 100G QSFP28 LR4 at about $200–285 (same price guide); short-reach multimode modules cost less than either.
- Installation. Field termination and testing cost about the same for both. Pre-terminated assemblies avoid most field work for either type; see pre-terminated fiber optic cable.
So the answer depends on how many links you have and how long they are. Inside one building with many short links and many ports, multimode often costs less overall. Over longer distances, or where the cable must carry the next two generations of equipment, single-mode costs less over its life, and many new data centres now use single-mode even between racks for that reason.
Which one to choose
| Project | Choose | Why |
|---|---|---|
| FTTH and any PON network | Single-mode (G.652.D; G.657.A1/A2 for distribution and drops) | PON optics and standards are single-mode only |
| Campus or industrial backbone, between buildings | Single-mode | Distances beyond what multimode reaches at 10G and above |
| Inside one building, links under 100–300 m, 1–10G | OM4 multimode, or single-mode if the cable must last | Cheap 850 nm optics; OM4 has headroom over OM3 |
| Data centre, rows and rooms | Single-mode for long and future 400G/800G links; OM4 for short in-row links | Matches the optics you plan to buy |
| Extending an existing multimode plant | The same OM grade as installed | Mixing grades limits the link to the lower grade |
Our guide on G.652.D vs G.657 fiber covers which single-mode grade goes where in an FTTH network.
Do not mix them in one link
A multimode fiber spliced or patched to a single-mode fiber loses most of the light entering the narrow core, and a single-mode transceiver on multimode fiber does not work reliably. Keep one fiber type end to end, including patch cords. Single-mode patch cords have yellow jackets and blue (UPC) or green (APC) connectors; laser-optimised multimode cords are aqua. The one standard exception is 1000BASE-LX or 10GBASE-LRM over installed multimode fiber, which needs mode-conditioning patch cords at both ends.
What to write in your BOM
Name the fiber on every line: “OS2 G.652.D” or “G.657.A2” for single-mode, “OM4” or “OM3” for multimode, together with the fiber count, construction and connector, for example “24F OM4 MPO trunk, Type B, 15 m”. Order the transceivers to match: SR modules for multimode, LR or longer for single-mode. Our SFP modules page lists the types and reaches, and the guide on sending an FTTH BOM lists the other fields that let us quote without back-and-forth.
Sources
- IEEE 802.3-2022, “IEEE Standard for Ethernet”, clauses on 1000BASE-SX/LX, 10GBASE-SR/LR/ER, 25GBASE-SR, 40GBASE-SR4 and 100GBASE-SR4 reach. standards.ieee.org
- ITU-T, “G.652: Characteristics of a single-mode optical fibre and cable”, August 2024. itu.int
- Fiber Optic Association, “Optical fiber”, reference guide. thefoa.org
- Fiber Optic Association, “Fiber optic cable color codes” (TIA-598 jacket and connector colours). thefoa.org
- ZeroLine Connect, “Fiber optic cable prices, October 2026”. connect.zerolineai.com
Next guide Fiber optic connector types: LC vs SC, UPC vs APC