Keycap Compatibility Checker
Keycap sets fail at the bottom row, not the letters. Tell it what you have and it lists the sizes the set has to include.
Every keycap size, and where it sits
One unit (1u) is 19.05 mm centre to centre. This table is the reference the checker runs on.
| Size | In millimetres | Where it normally sits |
|---|---|---|
| 1u | 19.05 mm | Letters, numbers, F-row, arrows |
| 1.25u | 23.8 mm | Bottom row modifiers on a standard layout |
| 1.5u | 28.6 mm | Tab, and outer modifiers on a Tsangan bottom row |
| 1.75u | 33.3 mm | Caps Lock, and right Shift on 65% and 75% boards |
| 2u | 38.1 mm | Backspace, and the zero on a number pad |
| 2.25u | 42.9 mm | Left Shift and ANSI Enter |
| 2.75u | 52.4 mm | Right Shift on full-size, TKL and standard 60% |
| 6.25u | 119.1 mm | The usual spacebar |
| 7u | 133.4 mm | Spacebar on a Tsangan bottom row |
Common questions
- How do I know if a keycap set will fit my keyboard?
- Check three things: the spacebar width, the bottom row modifier widths, and the right Shift. Those are where sets fail. The alphas fit almost any board, so a set that is described as compatible can still leave you with gaps at the bottom of the keyboard.
- What size is a standard spacebar?
- Most full-size, tenkeyless and standard 60% boards use a 6.25u spacebar. Many 65% and 75% boards, and enthusiast 60% boards, use 7u instead, or split the spacebar into two or three keys. One unit is 19.05 mm, so 6.25u measures about 119 mm.
- Why do keycap sets not fit 65% and 75% keyboards?
- Because those layouts squeeze an arrow cluster in beside the right Shift, which shrinks it from 2.75u to 1.75u. A base kit built for a full-size board has no 1.75u right Shift in it. Look for a set that lists a compact, 65% or multi-layout kit.
- What does 1u mean on a keycap?
- One unit, the width of a single letter key, which is 19.05 mm from the centre of one key to the next. Every other size is a multiple: a 1.25u modifier is a quarter wider, a 2u backspace is twice the width, a 6.25u spacebar is six and a quarter letter keys long.
- Do I need an ISO or ANSI keycap set?
- ANSI has a wide horizontal Enter and a 2.25u left Shift. ISO has a tall Enter shaped like a backwards L, a 1.25u left Shift and one extra key beside it. They are not interchangeable, and many base kits are ANSI only, with ISO support sold as an add-on kit.
Sizes here are the common case for each layout. Compact boards vary between makers, so count your own bottom row before ordering. More on what the sizes mean in the keycap buying guide, and on which board size suits you in the keyboard sizes guide.