The RJ21 Pinout and 25-Pair Colour Code, Explained

If you're terminating an RJ21 cable by hand — or just trying to work out which pair feeds which port — the 25-pair colour code is the thing you'll keep coming back to. It looks daunting the first time, but there's a simple logic underneath, and once it clicks you can read any Telco cable at a glance. Here's the full chart, and the bit of reasoning that makes it stick.

The logic behind the colours

Every pair is identified by two colours: a major (group) colour and a minor (pair) colour. There are five of each, and they cycle in a fixed order:

Major colours (in order): White, Red, Black, Yellow, Violet — one for each group of five pairs.
Minor colours (in order): Blue, Orange, Green, Brown, Slate — cycling within each group.

So pairs 1–5 are all White-something, pairs 6–10 are all Red-something, and so on. Within each group the minor colour steps through Blue, Orange, Green, Brown, Slate. That's the whole system — five groups of five, 25 pairs in total.

For each pair, the tip conductor carries the major colour with a minor stripe, and the ring carries the minor colour with a major stripe. So pair 1's tip is White/Blue and its ring is Blue/White.

The full 25-pair chart

Pin numbering below follows 258A: tip conductors on pins 1–25, ring conductors on pins 26–50. Pair N sits on pins N and N+25.

Pair	Tip (major / minor)	Ring (minor / major)	Pins (tip · ring)
1	White/Blue	Blue/White	1 · 26
2	White/Orange	Orange/White	2 · 27
3	White/Green	Green/White	3 · 28
4	White/Brown	Brown/White	4 · 29
5	White/Slate	Slate/White	5 · 30
6	Red/Blue	Blue/Red	6 · 31
7	Red/Orange	Orange/Red	7 · 32
8	Red/Green	Green/Red	8 · 33
9	Red/Brown	Brown/Red	9 · 34
10	Red/Slate	Slate/Red	10 · 35
11	Black/Blue	Blue/Black	11 · 36
12	Black/Orange	Orange/Black	12 · 37
13	Black/Green	Green/Black	13 · 38
14	Black/Brown	Brown/Black	14 · 39
15	Black/Slate	Slate/Black	15 · 40
16	Yellow/Blue	Blue/Yellow	16 · 41
17	Yellow/Orange	Orange/Yellow	17 · 42
18	Yellow/Green	Green/Yellow	18 · 43
19	Yellow/Brown	Brown/Yellow	19 · 44
20	Yellow/Slate	Slate/Yellow	20 · 45
21	Violet/Blue	Blue/Violet	21 · 46
22	Violet/Orange	Orange/Violet	22 · 47
23	Violet/Green	Green/Violet	23 · 48
24	Violet/Brown	Brown/Violet	24 · 49
25	Violet/Slate	Slate/Violet	25 · 50

The one thing to always check

The colour code is universal, but how tip and ring map onto specific ports is not guaranteed to be identical on every piece of equipment. Some gateways flip the tip/ring orientation, or number their ports in a way that doesn't start where you'd expect. Cisco, for instance, documents its own RJ21 pinout for the VG224 — and notes that the final pair isn't connected at all.

So treat this chart as the reliable map of the cable, then confirm the equipment against its own pinout before you punch down a whole panel. Five minutes with the manufacturer's pinout sheet saves an afternoon of testing reversed lines.

Why this matters for ordering

If you'd rather skip the punch-down entirely, this is exactly what a pre-wired (leaded) patch panel does for you — the 25 pairs are already terminated to the colour code and tested, so you plug in and go. And if you're making up your own runs, ordering cable wired to 258A means the colours land where this chart says they should.

Frequently asked questions

Skip the punch-down. Our leaded patch panels arrive pre-wired to the colour code and 100% tested. Prefer to make your own runs? Order RJ21 Cat3 cable wired to 258A, any length.