What is the difference between an RJ45 and an RJ11 jack?

An RJ45 jack is the 8-position, 8-contact (8P8C) modular socket used for Ethernet and PoE; an RJ11 jack is the narrower 6-position socket (typically 6P2C or 6P4C) used for analog telephone and DSL. The RJ45 body is about 11.68 mm wide versus about 9.65 mm for RJ11, carries four differential pairs wired to ANSI/TIA-568 T568A/T568B, and can integrate isolation magnetics. RJ11 carries one or two voice pairs on USOC wiring and does not support Ethernet.

Does an RJ11 plug fit in an RJ45 jack?

Physically a 6-position RJ11 plug can be pushed into the center of an 8P8C RJ45 jack because it is narrower, but it is not recommended. The RJ11 plug can splay or deform the outer contacts (positions 1, 2, 7 and 8) of the RJ45 jack and it provides no Ethernet connection. The reverse does not work at all: an 8P8C RJ45 plug is too wide to enter a 6-position RJ11 jack.

Can an RJ11 jack carry Ethernet?

No. 10/100BASE-T needs two pairs and 1000BASE-T needs all four pairs across eight contacts, while an RJ11 jack has only two or four contacts and USOC wiring. It cannot carry standard Ethernet or PoE. Use an 8P8C RJ45 jack for any data or PoE port.

Do RJ45 jacks need magnetics when RJ11 jacks do not?

Yes. An Ethernet RJ45 port requires isolation magnetics, either a discrete LAN transformer or an integrated-magnetics magjack such as VOOHU's SYT series, which are rated at 350 uH OCL, 2250 V DC isolation and 750 mating cycles over a -40 to +85 C range. An RJ11 telephone jack carries low-frequency voice and does not use Ethernet magnetics.

Home › Resources › RJ45 vs RJ11 Jacks

By VOOHU Electronics · Updated July 7, 2026 · ~8 min read

RJ45 vs RJ11 Jacks: Differences, Compatibility & How to Choose

An RJ45 jack and an RJ11 jack look like the same clear-plastic modular socket at a glance, but they differ in width, contact count, wiring and purpose. This VOOHU Electronics guide compares the two female modular sockets (母座), settles the "will an RJ11 plug fit an RJ45 jack?" question, and helps you specify the right jack for a data or voice port.

The short answer

An RJ45 jack is the 8-position, 8-contact (8P8C) modular socket used for Ethernet and PoE. An RJ11 jack is the narrower 6-position socket (typically 6P2C or 6P4C) used for analog telephone and DSL. They are not interchangeable: an 8P8C RJ45 plug is too wide to enter an RJ11 jack, while a 6-position RJ11 plug can be forced into an RJ45 jack but risks deforming the outer contacts and carries no Ethernet signal. Use RJ45 for data and PoE, and RJ11 for voice. VOOHU manufactures both jack families, so the guidance below is vendor-neutral on which one your port needs.

RJ45 vs RJ11 jack at a glance

Parameter	RJ45 jack (8P8C)	RJ11 jack (6P2C / 6P4C)
Positions / contacts	8 position / 8 contact	6 position / 2 or 4 contact
Body width (approx.)	≈ 11.68 mm (0.46 in)	≈ 9.65 mm (0.38 in)
Contact pitch	1.02 mm (0.040 in)	1.02 mm (0.040 in)
Interface standard	8P8C per IEC 60603-7	Registered Jack / USOC (TIA-968)
Wiring scheme	ANSI/TIA-568 T568A / T568B	USOC (reversed, center-out)
Primary use	Ethernet 10BASE-T → 10GBASE-T, PoE	Analog telephone (POTS), DSL
Signals carried	4 differential pairs + PoE (IEEE 802.3)	1–2 voice pairs (tip/ring)
Typical voltage	PoE up to 57 V DC (802.3bt)	≈ 48 V DC on-hook, ≈ 90 V AC ring
Isolation magnetics	Yes — discrete or integrated magjack	No

Widths and pitch are standard modular-connector dimensions (IEC 60603-7 / 8P8C and 6P families); wiring schemes per ANSI/TIA-568 and USOC.

Physical & mechanical differences

Both are modular jacks on the same 1.02 mm (0.040 in) contact pitch, which is why they look similar — but the RJ45 housing is wider to fit two extra positions. The RJ45 opening is roughly 11.68 mm across for eight contacts; the RJ11 opening is roughly 9.65 mm for six positions, of which only the inner two or four are loaded. That width gap is the whole story behind physical compatibility: the smaller plug can sit inside the larger socket, but not the reverse.

An RJ45 jack also has more to it mechanically. Because it terminates a 4-pair data cable, it is built for repeated mating and, in Ethernet designs, frequently carries built-in magnetics. Modular Ethernet jacks are specified for at least 750 mating cycles under IEC 60603-7, and VOOHU's integrated RJ45 magjacks are rated to that same 750-cycle durability. RJ11 telephone jacks, handling low-frequency voice, are mechanically simpler.

Electrical & signal differences

This is where the two truly diverge. An RJ45 Ethernet port drives four differential pairs (per IEEE 802.3) and, on PoE links, up to 57 V DC of bias power under IEEE 802.3bt. To keep that clean it needs isolation magnetics — either a discrete LAN transformer or an integrated-magnetics magjack built into the socket. An RJ11 jack carries a single analog voice pair (tip/ring) at roughly 48 V DC on-hook with about 90 V AC ringing, and uses no Ethernet magnetics at all.

VOOHU integrated RJ45 magjack — sourced specifications. VOOHU's SYT-series integrated-magnetics RJ45 jacks (e.g. SYT-320DNL, SYT511Q293AC1A8D057) are published at 350 µH OCL, 1CT:1CT turns ratio, 2250 V DC isolation, insertion loss ≤ 1.0 dB, common-mode rejection −30 dB, 750 mating cycles, and an industrial −40 to +85 °C range, in 1×1, 1×N and 2×N configurations with 90° or 180° mounting and green/yellow status LEDs. These are exactly the parameters an RJ11 jack does not need — and cannot provide.

Wiring: T568A/T568B vs USOC

RJ45 data jacks are wired to the structured-cabling standards ANSI/TIA-568 T568A or T568B, which assign the four twisted pairs to specific pin positions for balanced, low-crosstalk transmission. RJ11 telephone jacks use the older USOC scheme, wired from the center pins outward so that a narrower plug always lands on the active pair. Mixing the two schemes is a common field error — see our T568A vs T568B wiring guide for the RJ45 pinout in detail.

Compatibility: will they mate?

RJ11 plug into an RJ45 jack

It physically fits — the 6-position plug is narrower and drops into the middle of the 8P8C socket — but it is a bad idea. The RJ11 plug can push against and permanently splay the outer contacts (positions 1, 2, 7 and 8) of the RJ45 jack, causing intermittent Ethernet later, and it delivers no data connection in any case.

RJ45 plug into an RJ11 jack

This does not fit. The 8P8C plug is about 2 mm wider than the RJ11 opening and will not seat. Never force it.

Rule of thumb: a data port is always an RJ45 (8P8C) jack; a voice/DSL port is an RJ11 (6P) jack. If a socket must accept both a phone and an Ethernet plug in the field, specify a proper RJ45 jack and use adapters — do not rely on cross-plugging.

How to choose the right jack

Step 1 — What signal is on the port?

Ethernet or PoE → RJ45 (8P8C). Analog telephone or DSL → RJ11 (6P).

Step 2 — What speed / power?

10/100BASE-T uses two pairs; 1000BASE-T and multi-gig use all four pairs — both require an RJ45 jack. For PoE/PoE+/PoE++ you also need magnetics rated for the DC bias current; an integrated magjack simplifies this. See our RJ45 jack pinout for PoE.

Step 3 — Discrete or integrated magnetics?

For RJ45 data ports, decide between a separate LAN transformer plus a plain jack, or an all-in-one magjack. Contact plating and shielding also matter for signal integrity — our materials & plating guide covers the tiers.

Step 4 — Mechanical fit

Match port count and orientation (1×1, 1×N, 2×N; 90° vertical or 180° horizontal) to your PCB and panel. VOOHU offers standard, low-profile, offset, combination and waterproof RJ45 jacks alongside its RJ11 range.

Common mistakes

Teams repeatedly trip over the same issues when confusing these two jacks:

Forcing an RJ11 plug into an RJ45 jack. It deforms the outer contacts and creates intermittent faults that only appear months later.
Assuming a phone cable carries Ethernet. A 6-position RJ11 lead cannot deliver 1000BASE-T — Gigabit needs all four pairs on eight contacts.
Specifying RJ11 for a data port to save cost. False economy: no Gigabit, no PoE, no magnetics path.
Omitting magnetics on the RJ45 port. An Ethernet jack needs a discrete transformer or an integrated magjack; a bare jack will not pass compliance.
Mixing wiring schemes. RJ45 uses T568A/T568B, not the USOC scheme used for RJ11.

Spec'ing RJ45 or RJ11 jacks?

VOOHU Electronics manufactures standard, low-profile, offset, combination, waterproof and integrated-magnetics RJ45 jacks, plus RJ11 telephone jacks — female modular sockets for data and voice ports. Request datasheets or samples to match your speed, PoE and mounting needs.

Visit www.voohuele.com · Email olivia@voohuele.com · WhatsApp +86 133 5804 1040

Frequently asked questions

What is the difference between an RJ45 and an RJ11 jack?: RJ45 is the 8-position/8-contact (8P8C) modular jack for Ethernet and PoE; RJ11 is the narrower 6-position jack (6P2C/6P4C) for analog telephone. RJ45 is wider (≈11.68 mm vs ≈9.65 mm), carries four differential pairs wired to ANSI/TIA-568, and can integrate isolation magnetics. RJ11 carries one or two voice pairs on USOC wiring.
Does an RJ11 plug fit in an RJ45 jack?: Physically yes — the 6-position plug is narrower and slots into the center of the 8P8C socket — but it is not recommended: it can deform the outer contacts (positions 1, 2, 7, 8) of the RJ45 jack and gives no Ethernet link. An RJ45 plug will not fit an RJ11 jack because it is too wide.
Can an RJ11 jack carry Ethernet?: No. 10/100BASE-T needs two pairs and 1000BASE-T needs all four pairs across eight contacts. An RJ11 jack has only two or four contacts and USOC wiring, so it cannot carry standard Ethernet or PoE. Use an 8P8C RJ45 jack for data.
Do RJ45 jacks need magnetics when RJ11 jacks do not?: Yes. An Ethernet RJ45 port requires isolation magnetics — a discrete LAN transformer or an integrated magjack such as VOOHU's SYT series (350 µH OCL, 2250 V DC isolation, 750 mating cycles, −40 to +85 °C). An RJ11 telephone jack carries low-frequency voice and uses no Ethernet magnetics.