The keycap calibration rate was defined by the switch switch inventor, Cherry, which although not a standard defined as such, can be considered standard because it is a design on which all others are based. For this reason, the unit of measurement key is known as «Cherry's profile", Or sometimes"OEM profile«.
Standard size of keycap for machine keyboards
Following the Cherry profile, standard size and depth of range of key keyboards are available 1 × 1 (18mm), and which changes little in height and shape, something that doesn't always interfere with compatibility.
Compatibility problem is usually with special keys, such as CTRL, ALT, space bar, and SHIFT. Here you have a size that is considered normal, based on the Cherry profile.
As you can see, the special buttons have a standard size of 1 × 1.25, and SHIFT 1 × 2.25 and space bar 1 × 6.25, and yet there are many keyboards that CTRL, ALT and WIN have their key keys that do not match, as standard says all three should be the same size.
As for the space bar, these are their standard dimensions according to the Cherry profile.
What you should check to see if they are compatible with your keyboard
The first thing to look for is if the key buttons you are willing to buy have the same anchorage for your keyboard. Machine key locks are usually in cross-center position, Cherry style and size, but you must be careful because in the end not everyone used the same system. Also be careful if your keyboard is low profile or hybrid, because the anchorage changes too.
After this, you need to make sure that your current key keys have the size of the Cherry profile. If they are 18 x 18 mm at their widest point, then they are of the right size, and as a general rule, any set of codes that fit these sizes will work for you. With everything and everything, you'll have to make sure the size of the CTRL, ALT, SHIFT and space bar, as well as the ENTER key that, as you know, on the ANSI keyboards is different from the others.
Unfortunately, you'll have to measure your keyboard's keys and know the size of the buttons you want to buy in order to know if they'll fit. Fortunately, manufacturers know this and in almost all cases show the size of every button they sell.
So you know, even though the anchorage is the same, not all keys are compatible with all keyboards, and if you want to change your own, you'll have to balance to verify it.