One of the most common questions on GeekHack and /r/mechanicalkeyboards is, “Will this keycap set fit my keyboard?” I know I asked this question countless times when I got into mechanical keyboards, and I still remember how daunting it was. If just one out of 100+ keycaps is wrong, your money’s been wasted. Do you want a keyboard that’s missing even one keycap? I know I don’t.

Fortunately, there’s an easy trick, and I’m going to teach it to you in this post. Once you’ve learned and practiced the trick, it’ll become second nature to tell if a keycap set fits your board. Soon you’ll be answering the question for other people instead of asking it yourself.

(This post is tailored for people with Cherry MX keyboards. While much of the information applies to other switches like Topre, there are other specific issues not discussed here. I’ll publish similar guides for Topre, ALPS, and buckling spring soon.)

So what’s the trick? The trick is learning the standard layout.

Most modern mechanical keyboards are standard, meaning they have this exact 104-key layout* (click to enlarge):

*Note: Your keyboard does not have to be full-size to be standard. For example, the CM Storm QuickFire Rapid tenkeyless and the Poker II 60% are both standard despite having fewer keys. The important thing is that the keys they do have are standard.

The standard layout was popularized in the late 1990s when the Windows key came onto the scene. It’s not just called “standard” because it’s common, though. It’s standard because it’s defined in the American National Standards Institute’s ANSI-INCITS 154-1988 spec.

If your Cherry MX keyboard is standard, almost any new aftermarket MX keycap set will fit it. Period. Since the standard layout is the most common layout, keycap manufacturers and group buy leaders always make sure their keysets fully cover the standard layout. (Buying vintage keycap sets is a whole different ballgame, though.)

Standard layout = any current retail keycap set will work. Easy enough, right? But how do you know if your board is standard?

By using your eyes to perform these three tests:

Check the spacebar row. A standard layout has a 1.25x – 1.25x – 1.25x – 6.25x – 1.25x – 1.25x – 1.25x – 1.25x bottom row. That means it has three equally sized modifiers to the left of the spacebar and four to the right, each one 1.25x times the width of a normal letter key. The spacebar is 6.25 units. Anytime you see three equal size modifiers on the left of the spacebar, and four equal size modifiers on the right, it’s standard. If there’s a different number of modifiers, or if they’re not all the same width, it’s not standard.

A standard layout has a 1.25x – 1.25x – 1.25x – 6.25x – 1.25x – 1.25x – 1.25x – 1.25x bottom row. That means it has three equally sized modifiers to the left of the spacebar and four to the right, each one 1.25x times the width of a normal letter key. The spacebar is 6.25 units. Anytime you see three equal size modifiers on the left of the spacebar, and four equal size modifiers on the right, it’s standard. If there’s a different number of modifiers, or if they’re not all the same width, it’s not standard. Check the Shift row. The next row up has Shift, Z through /, then another Shift, and the whole row is the same width as the ones above and below it. If there are any other keys or if this row is a different length, for example because it has a short right shift, then it’s not standard.

The next row up has Shift, Z through /, then another Shift, and the whole row is the same width as the ones above and below it. If there are any other keys or if this row is a different length, for example because it has a short right shift, then it’s not standard. Check the Caps Lock row. The next row up has Caps Lock, A through ‘, and then Enter. Caps Lock must be full-touch, not stepped, and enter must be a plain rectangle, not a Big-Ass enter or some other shape. Does that all check out?

If these 3 tests pass, and your keyboard looks like the photo above, your keyboard is standard. Congratulations—buy any new keycap set you want. It’ll work.

If one or more tests fail, then your keyboard isn’t standard, and your life gets more complicated. You might still be able to use the keycap set you have in mind, but more investigation is needed. Here are the most common ways your keyboard might be non-standard:

It’s winkeyless: Does your keyboard’s bottom row look like this, with just Ctrl and Alt on either side of the spacebar? If so, your keyboard is probably vintage/used, from before the time of the Windows key, or a custom build. It’s called a Winkeyless layout, with a 1.5x – 1.5x – 7x – 1.5x – 1.5x bottom row. Caps Lock will almost always be stepped, too. If your keyboard is like this, you need to find out whether the keycap set has 1.5x mods, a stepped caps lock, and a 7x spacebar, frequently called a Tsangan kit. In group buys, Tsangan kits are commonly sold as “child kits” for about $15-20 extra. But unfortunately, Tsangan kits aren’t always available, especially if the keyset isn’t from a group buy.

Does your keyboard’s bottom row look like this, with just Ctrl and Alt on either side of the spacebar? If so, your keyboard is probably vintage/used, from before the time of the Windows key, or a custom build. It’s called a Winkeyless layout, with a 1.5x – 1.5x – 7x – 1.5x – 1.5x bottom row. Caps Lock will almost always be stepped, too. If your keyboard is like this, you need to find out whether the keycap set has 1.5x mods, a stepped caps lock, and a 7x spacebar, frequently called a Tsangan kit. In group buys, Tsangan kits are commonly sold as “child kits” for about $15-20 extra. But unfortunately, Tsangan kits aren’t always available, especially if the keyset isn’t from a group buy. It’s got some extra keys: For example, many Ducky keyboards have four extra media keys in the upper-right corner. While the rest of the keys will fit fine, you might not be able to fully cover a board like this unless your desired set includes the necessary extras.

For example, many Ducky keyboards have four extra media keys in the upper-right corner. While the rest of the keys will fit fine, you might not be able to fully cover a board like this unless your desired set includes the necessary extras. It’s an unusual form factor: For example, see the Leopold FC660M , which uses two left shifts, or the Noppoo Choc Mini, which is just completely hopeless.

For example, see the Leopold FC660M , which uses two left shifts, or the Noppoo Choc Mini, which is just completely hopeless. It’s an older Leopold: Leopolds older than the FC750R/FC900R appear fully standard but have non-standard spacebar stem spacing, which means most aftermarket spacebars are not compatible.

Leopolds older than the FC750R/FC900R appear fully standard but have non-standard spacebar stem spacing, which means most aftermarket spacebars are not compatible. It’s ISO: ISO (European layout) keyboards are technically “standard” too, but only if you’re in Europe. 🙂 If you have an ISO keyboard, you’ll always want to check that your desired keycap set includes ISO keys, which unfortunately is not always the case.

ISO (European layout) keyboards are technically “standard” too, but only if you’re in Europe. 🙂 If you have an ISO keyboard, you’ll always want to check that your desired keycap set includes ISO keys, which unfortunately is not always the case. It’s got a wack bottom row: Some boards like Corsairs and the Quickfire TK are mostly standard but have wacky bottom rows. For example (click to enlarge):

See how there are not three evenly sized mods to the left of the spacebar and four to the right? There are a bunch of 1x mods mixed in there. In cases like these, you’re most likely out of luck because very few keysets come with alternative modifiers / spacebars beyond possibly Tsangan kits.

Once you understand what the standard layout is and get accustomed to rapidly performing the tests I described above, you’ll find that you quickly get better at determining whether a keycap set will fit a board. The more you run through the tests, the better you’ll get at using your eyes critically and being able to determine key compatibility with a single glance. It’s not unlike how artists have to re-learn how to see lines and shadows. At first it’s very difficult, but the more you practice the better you get. Really, there are only a few major patterns and I’ve described them all here (standard, winkeyless, standard with extra keys, unusual form factor, and standard with messy bottom row).

And if you’re still not sure… post in the comments and I’ll help you. 🙂 (EDIT: I also strongly recommend checking /r/mechanicalkeyboard’s Key Reference Guide to see if there are any considerations for your specific board.)