How to Read a Tartan Thread Count

Guide · Updated 20 September 2026

Letter, then count

A thread count is not a picture of the cloth; it is the instruction for warping a loom. Each token names a colour and a number of threads, and the run of tokens is one repeat of the pattern — the sett. Because the unit is the thread, the notation says nothing about how big the cloth will be: that comes from the yarn. The same sett in a fine cotton and a heavy worsted gives a small check and a large one.

The letters are the traditional register codes, and The Plaid Studio reads them:

Those hexes are only what a code looks like when nothing else says otherwise — a starting colour, not the definition of the shade. Register books and mills differ on exactly which red is red, and you are expected to set your own.

A letter that is not in the table is not an error. Setts in the wild use house codes — an F for a field colour, a Q for something a mill named itself. The parser keeps an unrecognised code as its own colour and asks you to map it, rather than refusing the paste or silently guessing. Only a token longer than three letters is rejected.

The mirror, and why there is no mirror mark

Most tartan setts are reflective: the sequence runs to a pivot and comes back. The notation does not mark the pivot, because it does not need to — the first and the last stripe are the mirror axes. They are counted once; everything between them appears twice.

So K4 B24 K2 W6 is not four stripes, it is six, and 62 threads:

• written: K4 B24 K2 W6 — 36 threads
• woven: K4 B24 K2 W6 K2 B24 — 62 threads, then it starts again

One consequence worth knowing before you hand a sett to a loom: a pivot stripe with an odd thread count puts the mirror axis halfway through a thread. It is not fatal, but it is the sort of thing a weaver notices and a drawing tool does not, so the studio flags it.

Not every check is mirrored. A repeating sett runs straight round with no reflection, and the notation says so with a marker: ..., | or (rep) anywhere in the string switches the sett from mirrored to repeating. Gingham, buffalo check, windowpane and madras are all repeating; a clan-style tartan is usually reflective.

Reading real cloth off its count

Once the notation is readable, the difference between two cloths stops being a matter of taste and becomes something you can see written down. These are the counts behind our own pattern pages:

Three things fall out of that table. The windowpane is one wide ground and one narrow line — G72 A4 is the whole idea of the cloth. The Prince of Wales is a glen check with four threads of a third colour added at the end of the repeat: one token is the entire difference between the two cloths. And madras has no two runs alike, which is why it reads as a happy accident even though every band is still a whole number of threads.

Those counts use house codes — G for the ground, F for the field, A and B for accents — which is exactly the case described above: the G and A happen to be in the register table, the F is not, and it works the same either way because the colours are set alongside the count.

Typing one in

The notation is more forgiving than it looks. Separators can be spaces, commas, semicolons or dashes, or nothing at all: K4 B24 K2 W6, K4,B24,K2,W6 and K4B24K2W6 all parse the same. Case does not matter. A slash between colour and count is allowed, K/4 B/24, and a hex colour must use it — #c81428/24 — so the count cannot be read as more hex digits.

If you know the rhythm but not the colours, type the numbers alone: 4 24 2 8 makes four stripes of those counts in placeholder greys, to be coloured by clicking them.

What will actually be refused: a colour code longer than three letters, a colour with no count after it, a count of zero, and an empty sett. Under eight threads in total is too little to be cloth and gets a warning; over two thousand is fine to design but the preview is downsampled.

Frequently asked questions

What do the numbers in a tartan sett mean?

Each number is a count of threads for the colour beside it, in the order they are warped on the loom. B24 is twenty-four threads of blue. It is a count, not a width: how wide those twenty-four threads end up depends on the yarn.

Why does a tartan sett look half as long as the cloth?

Because a reflective sett is written once and mirrored. The first and last stripe are the mirror axes and appear once; every stripe between them appears twice, so the woven repeat is nearly double what is written.

How do I write a sett that does not mirror?

Add ..., | or (rep) anywhere in the string. That switches it to a repeating sett, which runs straight round — the normal case for gingham, buffalo check and madras.

What if a sett uses a letter I do not recognise?

Keep it. Mills and pattern books use their own codes, so an unknown letter is treated as a colour of its own and you map it to the shade you want; nothing is guessed for you.

Does a thread count tell me the size of the check?

No, and this is the most common misreading. The count is in threads; the physical size comes from the yarn count. Set the yarn, and the same sett can be a shirting check or a blanket.