Standard MX keycap dimensions start with the grid: a 1u cap sits on 19.05 mm (0.75 in) centres and measures about 18 mm square at the base, leaving roughly a millimetre of gap. Inside, the socket is a cross 4.1 mm wide with 1.17 mm arms, per Cherry’s 1983 keycap specification. Height depends on profile, from about 7.4 mm for DSA to 16.5 mm for SA.
MX names the mount, not the shape. Any cap with that cross socket fits a Cherry MX switch or clone, from a low Cherry-profile alpha to a tall SA space bar. The numbers fall into three groups: grid footprint, stem socket and profile height. Some are manufacturer specifications and some community measurements; the table keeps them apart.
MX keycap dimensions at a glance
| Dimension | Figure | Type of evidence |
|---|---|---|
| Grid pitch, centre to centre | 19.05 mm (0.75 in) | Conversion of the ¾ in unit |
| 1u base, generic | 17.9 to 18.2 mm square | Three caps measured by one Deskthority member |
| 1u base, one named cap | 18.5 × 18 mm | Jelly Key Cherry-profile R1 |
| 1u top, one named cap | 10.7 × 14 mm | Jelly Key Cherry-profile R1 |
| Socket cross width | 4.1 mm, +0.05 mm | Cherry keycap specification, 1983 |
| Socket arm width | 1.17 mm, ±0.02 mm | Cherry keycap specification, 1983 |
| Socket, Signature Plastics | 4.04 mm cross, 1.19 mm arms | SP figures recorded by Deskthority |
| Switch stem arms | 1.10 mm north-south, 1.25 mm east-west | Cherry switch specification, per ThereminGoat |
| Switch stem height | About 3.7 mm | Deskthority |
| Travel under the cap | 4 mm total, 2 mm pre-travel | Cherry MX2A Red specification |
| Cap height | About 7.4 mm (DSA) to 16.5 mm (SA) | Deskthority; Das Keyboard |
The socket figures come from Deskthority’s keycap mount reference, which cites Cherry’s MX keycap specification and records Signature Plastics’ slightly different numbers. Travel figures are Cherry’s, from its MX2A Red product page: the cap moves 2 mm before the switch registers, then 2 mm more to bottom-out.
How big is a 1u MX keycap?
A 1u MX keycap is about 18 mm square at the base and sits on a 19.05 mm grid, so roughly 1 mm of every unit is gap between caps. The top is smaller and, on sculpted profiles, not square: Jelly Key gives its Cherry-profile R1 cap a 10.7 × 14 mm top over an 18.5 × 18 mm bottom.
The 19.05 mm figure is a conversion, not a metric standard. Deskthority’s unit reference puts full-size board units at about 19 mm or ¾ inch, notes ISO 1091 allowed 19 mm ± 1 mm until the standard was withdrawn in 1994, and says caps are made fractionally smaller than their unit to leave a gap. A community measurement of three 1u bases found 18.2, 18.0 and 17.9 mm square.
That spread matters less than it looks. Caps a few tenths of a millimetre apart at the base still sit on the same switch centres; only the gap between keys shifts slightly. The Jelly Key Cherry-profile write-up anchors the table because it is one of the few maker pages publishing bottom, top and height together, but it describes one product, not a Cherry drawing.
For wider keys, multiply the unit count by 19.05 mm and subtract roughly a millimetre. Deskthority’s space bar catalogue lists the Cherry MX 6.25u bar at 118 mm against 119.06 mm of grid, and records 6.25u bars with stabiliser mounts 50, 42.5 or 40 mm either side of centre, so width alone never guarantees fit. The full width chart and bottom-row variants are in keycap sizes in mm and units.
What are the MX stem socket dimensions?
The MX socket is a plus-shaped slot 4.1 mm across, with a tolerance of +0.05 mm, and arms 1.17 mm wide, ±0.02 mm, per Cherry’s 1983 keycap specification as recorded by Deskthority. That makes each arm about 1.465 mm long. Signature Plastics lists its socket as 0.159 in (4.04 mm) across with 0.047 in (1.19 mm) arms.
The switch stem filling the slot is not its mirror image. Deskthority’s Cherry MX page describes the stem’s east and west arms as around 1.25 to 1.30 mm thick and the north and south arms as 1.05 to 1.10 mm, making the mount only 180° rotationally symmetric. Switch reviewer ThereminGoat, writing for Artisan Collector, gives Cherry’s original switch specification as 1.10 mm north-south and 1.25 mm east-west.
Side by side, the two drawings explain retention. The east-west arms are wider than the 1.17 mm slot, so those faces carry the grip; Telcontar’s Cherry MX reference puts the overlap at 0.07 mm on two of four sides. The north-south arms are narrower, and ThereminGoat argues that clearance lets trapped air escape as the cap goes on. Nothing clips or latches. A keycap stays put on a few hundredths of a millimetre of interference, and that margin separates a cap that lifts off cleanly with a wire puller from one that fights you.
Why do some MX keycaps crack or come loose?
A crack or loose cap means the interference between stem and socket is out of range: too much and the socket’s gripping faces split, too little and the cap rocks or lifts off. ThereminGoat’s survey of 200 switch stems from 17 manufacturers found every cross span under the 4.10 mm slot, but most east-west posts wider than the 1.17 mm keycap figure.
Only 10 of the 200 met Cherry’s keycap specification on those measurements. Against Cherry’s switch specification, which allows wider east-west posts, the picture improves: 8 switches exceeded the east-west width or span, three from SP Star, and 3 exceeded the north-south width, all from Tecsee. ThereminGoat estimates only about 4% of switches pose a risk.
Kailh Box switches carried the cap-cracking reputation. The article cites early Box stems at around 1.32 mm across the east-west posts, against roughly 1.23 mm on samples collected around 2020, and argues the old warning should be retired. Hand-cast resin artisans vary more than moulded caps, though, and the author still suggests keeping valuable ones boxed, not on a board.
If a cap rocks rather than grips, work through how to fix keycap wobble, which isolates cap, switch and stabiliser in turn.
How tall is an MX keycap?
MX keycap height runs from about 7.4 mm for DSA to 16.5 mm for SA, because height belongs to the profile, not the mount. Deskthority records DSA at 0.291 in (7.39 mm); Das Keyboard lists Cherry profile at 9.4 mm and OEM at 11.9 mm. Sculpted profiles change height from row to row, so one number per profile is a simplification.
| Profile | Height quoted by Das Keyboard | Other published figure |
|---|---|---|
| DSA | 7.6 mm | 7.39 mm (0.291 in), Deskthority |
| G20 | 7.6 mm | None cited here |
| XDA | 9.1 mm | None cited here |
| Cherry | 9.4 mm | About 10.2 mm max, Jelly Key R1 |
| OEM | 11.9 mm | None cited here |
| KAT | 13.5 mm | None cited here |
| Tai-Hao | 14.88 mm | None cited here |
| SA | 16.5 mm | None cited here |
Das Keyboard’s profile overview gives one figure per profile without naming the row or measuring point, so read it as a ranking, not a drawing. Deskthority’s DSA page is the attributable anchor for the low end. For row-by-row heights and vendor row labels, see keycap row codes and profile heights.
Socket depth and stem height
No source cited here publishes a socket depth, so treat any single figure with suspicion, though what is documented constrains it. Deskthority puts the MX stem’s cross at around 3.7 mm tall, on a platform that descends inside the switch. Jelly Key says after reserving the minimum depth for attaching to the switch, its R1 cap has under 5 mm of interior left for detail, and its redesign lowered the stem base height to 1.08 mm.
Stem height is also where older Cherry parts break compatibility. Deskthority records that Cherry M8 switches share MX’s lateral cross dimensions but use a shorter stem, making the caps incompatible. Cherry built an MX-M8 adapter switch, and Telcontar notes its plunger is extended in height by 1.5 mm.
What dimensions should you use to model or 3D print an MX keycap?
Start from Cherry’s socket figures and add clearance for your printer. The open-source KeyV2 OpenSCAD library defaults to an 18.16 mm square base, a top 6 mm narrower and 4 mm shorter front to back (12.16 × 14.16 mm), 1.5 mm walls, and a cross that digs 4 mm into the stem, with 0.35 mm of stem slop and 0.2 mm of inner slop.
The comments in KeyV2’s settings file are the useful part: raise the stem slop “if your keycaps stick in the switch”, and lower the inner slop “if your keycaps are falling off”. Its stem functions model the outer stem as 7.2 × 5.5 mm before slop is subtracted, and its Cherry profile, which the code describes as “based off GMK keycap set”, keeps the 18.16 mm base under an 11.85 × 14.64 mm top.
Treat those as printing defaults, not manufacturing tolerances. Cherry specifies socket arm width to ±0.02 mm; KeyV2 instead lets you tune clearance until a printed cap grips your switches. For production wall figures to compare with the 1.5 mm default, keycap wall thickness by material lists three named sets that each advertise exactly 1.5 mm.
FAQ
is mx a keycap profile or a stem type
MX is a stem type, not a profile. It names the cross-shaped mount Cherry introduced with its MX switches, and any cap with the 4.1 mm cross socket fits an MX-style switch. Cherry, OEM, SA, DSA, XDA and KAT are profiles, setting height and sculpt. A Cherry-profile cap and an SA cap can share an identical socket.
do mx keycaps fit kailh choc switches
No for the original Choc V1, yes for Choc V2. Kailh’s Choc V1 (PG1350) uses a proprietary mount on a smaller 18 × 17 mm key spacing, so MX caps will not seat. Choc V2 (PG1353) moved to an MX-compatible keycap mount, per Deskthority, though a tall MX profile undoes much of a low-profile board’s point.
how tall is an mx switch stem
The cross on a Cherry MX stem is about 3.7 mm tall, per Deskthority, and sits on a platform that descends inside the switch housing. Older Cherry M8 switches share the MX cross’s lateral dimensions but have a shorter stem, so M8 and MX keycaps are not interchangeable.
can you rotate mx keycaps 90 degrees
Not reliably. The switch stem’s cross is only 180° rotationally symmetric, its east and west arms thicker than its north and south arms, and Deskthority notes keycaps do not always fit sideways as a result. Test one cap on the actual switch before planning a rotated layout.
