What size slipmat do you need?
A twelve inch record is 302 mm across. The mat should sit just inside it.
One size covers almost every turntable: around 295 to 300 mm across, to sit just inside a twelve inch record. A twelve inch LP is 302 mm, so a 298.5 mm mat leaves 1.75 mm of record overhanging all the way round and nothing to catch the edge. Ten and seven inch records sit well inside that, which is why the same mat handles all three. The only real check is that your platter is a standard twelve inch one.
Size is the one specification where a mat can be plainly wrong rather than merely worse, and it is also the one with a single right answer for nearly everybody.
What size slipmat do you need?
Around 295 to 300 mm across, which covers essentially every twelve inch turntable made.
There is no range of sizes to choose between in the way there is with thickness or density. A mat is sized to sit just inside a twelve inch record, and almost all of them do, within a few millimetres of each other. Ours is 298.5 mm.
What size is a twelve inch record?
302 mm, not 304.8 mm.
Twelve inches would be 304.8 mm exactly, but a standard twelve inch LP is pressed slightly under nominal, at about 302 mm. That figure, not the one implied by the name, is what a mat has to fit inside. Getting this wrong by three millimetres is how a mat ends up visible past the edge of the record.
Why not make the mat the same size as the record?
Because the edge is where everything goes wrong.
If the mat matched the record exactly, any tiny off-centring would leave felt sticking out on one side. That edge then catches your fingers when you lift the record, catches the record itself when you drop it on, and is the first part of the mat to fray. Worse, when cueing, a protruding edge gives the record something to snag against as it turns.
So a mat is made a few millimetres under, and the record overhangs all the way round. With a 298.5 mm mat and a 302 mm record the overhang is (302 − 298.5) ÷ 2 = 1.75 mm on every side. Enough to be certain the felt is covered, little enough that the record is still fully supported out to its playable edge.
What about ten inch and seven inch records?
They sit well inside the mat, and that is fine.
The same arithmetic, run the other way:
- Twelve inch, 302 mm. 1.75 mm of mat inside the record edge.
- Ten inch, 254 mm. 22.25 mm of mat showing all the way round.
- Seven inch, 178 mm. 60.25 mm of mat showing.
A ring of exposed felt around a smaller record is not a problem. Nothing catches, because the exposed part is outside the record rather than under it, and the disc is supported across its whole underside. This is why nobody sells a seven inch slipmat for ordinary use: a twelve inch mat handles singles perfectly, and a smaller one would leave the platter rim bare.
Seven inch singles do bring their own quirk, which is that many need a 45 adapter for the large centre hole. That is a spindle question rather than a mat one.
Does it fit your platter?
If your turntable plays twelve inch records, yes, almost certainly.
Platters are built around the record they carry, so a twelve inch deck has a platter somewhere between about 290 and 305 mm. A 298.5 mm mat sits flat on all of them: a little inside the rim on the larger ones, a little over it on the smaller ones, and neither matters because felt that slightly overhangs a platter rim is still fully supported where the record is.
The exceptions are real but narrow: suitcase and portable players sometimes use a platter well under twelve inches, and a few decks have a raised rim or a recessed well that a full-size mat will not sit into. Both are visible at a glance.
What if the mat is too big?
Then it shows past the record, and the problems in the section above arrive.
A mat noticeably over 302 mm will be visible as a felt ring outside the record, will catch when you lift records off, and will fray at the exposed edge. It is also the giveaway that a mat was cut as a generic disc rather than sized for a record.
Cutting one down yourself is not worth attempting. Felt cut without a press leaves a ragged edge that sheds fibre immediately, and fibre on records is the one thing a mat is supposed to prevent.
What size is ours?
298.5 mm across and 3.18 mm thick, which is where every figure on the spec page starts.
The diameter is chosen for the 1.75 mm overhang above. The thickness is chosen because 21oz felt, which is 712 g/m², reaches an ordinary needled-felt density of about 0.22 g/cm³ at that depth. The reasoning on thickness, including how much it moves your tonearm, is in does slipmat thickness matter.
How do you check in thirty seconds?
- Put a record on the platter. If it is a twelve inch deck, a 298.5 mm mat fits.
- Look at the platter rim. A raised lip or a recessed well is the only thing that stops a flat mat sitting flat.
- Check the platter is not under 290 mm. Portable and suitcase players are where this turns up.
If all three pass, size is settled and the decisions left are density, thickness and what is printed on it. Ours ship flat in a record jacket rather than rolled, because felt keeps a curl once it has been given one, and a curled mat behaves like a warped record. The rest of the care is in how to clean a slipmat.
Questions
- What size slipmat do I need?
- Around 295 to 300 mm across. That covers essentially every twelve inch turntable. Ours is 298.5 mm.
- What size is a 12 inch record?
- About 302 mm, not the 304.8 mm that twelve inches would imply. Records are pressed slightly under nominal, and 302 mm is the figure a mat has to fit inside.
- Why is a slipmat smaller than the record?
- So the record overhangs all the way round. A protruding felt edge catches your fingers lifting the record, catches the record going on, snags while cueing, and is the first part to fray.
- How much smaller should the mat be?
- A few millimetres. With a 298.5 mm mat under a 302 mm record the overhang is 1.75 mm on every side, which is enough certainty with no wasted support.
- Will a 12 inch slipmat work with 10 inch records?
- Yes. A 254 mm ten inch record leaves 22.25 mm of mat showing around it. The exposed ring is outside the record, so nothing catches and the disc is fully supported.
- Will a 12 inch slipmat work with 7 inch singles?
- Yes. A 178 mm seven inch leaves 60.25 mm of mat showing. Nobody makes a seven inch slipmat for ordinary use because a twelve inch one handles singles and a smaller one would leave the platter bare.
- Do I need a different mat for 45s?
- No. The only seven inch complication is the large centre hole, which needs a 45 adapter, and that is a spindle matter rather than a mat one.
- Will it fit my platter?
- If your turntable plays twelve inch records, almost certainly. Twelve inch platters run between about 290 and 305 mm, and a 298.5 mm mat sits flat on all of them.
- When will a slipmat not fit?
- Portable and suitcase players with platters well under twelve inches, and decks with a raised platter rim or a recessed well a flat mat cannot sit into. Both are obvious at a glance.
- What happens if the mat is too big?
- It shows as a felt ring outside the record, catches when you lift records, and frays at the exposed edge.
- Can I cut a slipmat down to size?
- Not well. Felt cut without a press leaves a ragged edge that sheds fibre straight away, and fibre on records is what a mat exists to prevent.
- What size is yours?
- 298.5 mm across and 3.18 mm thick, in 21oz felt, which is 712 g/m².