Keyboard layouts explained: key blocks, ANSI vs ISO, and what a percentage hides

Five of them, and once you can see them the whole naming mess resolves. In the middle sits the alphanumeric block, the letters and the number row, which no keyboard drops. Around it are the modifiers: Shift, Ctrl, Alt, the Windows or Command key, Caps Lock, Tab, Enter and the spacebar. Along the top runs the function row, F1 to F12, usually with Escape at its left end. To the right of the letters is the navigation cluster, meaning Insert, Delete, Home, End, Page Up and Page Down, with the four arrow keys sitting below it in an inverted T. Furthest right is the number pad.

A full-size board keeps all five. Tenkeyless drops the number pad, which is where the name comes from, since the pad is ten digit keys plus its operators. Below that the compression gets more aggressive: the navigation cluster is the next thing to go, usually surviving as a column beside the arrows or vanishing into a modifier, and the function row is the last thing standing before a board becomes genuinely small.

That ordering is not arbitrary. Blocks disappear roughly in the order that a typical person stops touching them, which is why the letters are safe and the number pad is the first casualty. Whether it matches how you personally work is the actual question, and the article written to answer it is Full-size, TKL or compact: which keyboard size should you get?

IBM's Enhanced Keyboard, in 1985, and it has barely moved since. It shipped with 101 keys in the US layout and 102 internationally, and it is the machine that put the function row along the top edge rather than in a block beside the letters, gave Insert and Delete and the page keys their own cluster, and arranged the four arrows in the inverted T that every keyboard on your desk still uses.

Deskthority's entry on it and Sharktastica's history of the design agree on what happened next: the layout became the industry standard and survives in an extended 104 and 105-key form, the extension being the Windows keys and the menu key added in the mid-1990s. Forty years is a long time for an interface decision to hold.

This matters for a practical reason rather than a nostalgic one. Because everything descends from one 1985 arrangement, key sizes and positions are consistent enough across brands that a keycap set made by a company you have never heard of will usually fit a board made by a company that has never heard of them. The compatibility you take for granted is an inheritance, and the boards that break it are the ones that departed from the 1985 grid.

The Enter key and the left Shift, and that is very nearly the whole of it. Logitech's own explainer sets it out: an ANSI full-size board has 104 keys with a wide horizontal Enter and a long left Shift, while an ISO board has 105 with a tall L-shaped Enter and a shorter left Shift that makes room for one extra key beside it. Akko's guide gives the same figures and adds the smaller sizes, where the gap holds steady at one key: 87 against 88 at tenkeyless, 68 against 69 at 60%.

An ISO board also carries a key marked AltGr where an ANSI board has a second Alt, and that legend is the physical half of the story rather than the whole of it. What the key actually does is decided by the software layout, not by the board: Microsoft's own documentation describes the behaviour as belonging to "keyboard layouts that appropriate the right alt key for altGr", and Logitech qualifies its own AltGr note as Windows-only. Select US-International on an ANSI keyboard and you have AltGr with no ISO hardware anywhere near your desk; run a plain US layout on an ISO board and the same key is a plain right Alt.

Logitech's rough geography is that ANSI covers the United States, Canada, Australia and a good deal of Asia, while ISO is the European and British standard.

Neither is better and you almost certainly want whichever one your country sells you, since the legends have to match the characters your operating system produces. Where the two standards actually stop being interchangeable is narrower than it sounds, and Logitech is careful about it: asked whether the keycaps swap, it answers "Generally, no", and locates the problem at the Enter, Shift and surrounding keys. It separately lists the keys that are much the same on both, which is most of them. Four positions do the damage: Enter, the left Shift, the extra key beside that Shift, and where the backslash sits.

Four positions are enough, because a keycap set is sold as a set. Lemokey, a Keychron brand, puts it on its own product pages without hedging: an ISO keycap set is not compatible with any ANSI set, and the reverse, which is why it sells them as separate per-language variants. So the buyer-facing answer holds. A set bought for one standard will not fit the other, and you should buy for the board you own.

What actually bridges the gap is a conversion kit, sold separately from the set. Krome Keycaps sells individual ISO Enter caps and full ANSI-to-ISO conversion kits sized for 60%, 65%, 75%, 96% and full-size boards, which is the route to take if you have fallen for a set cut for the wrong standard. Akko adds the commercial background: ANSI sets are everywhere and ISO sets are comparatively rare, so the conversion usually runs in one direction. If replacing your keycaps some day matters to you, that is a real argument, and it is close to the only one either standard has over the other.

Because a percentage describes roughly how much width a board keeps, and nobody administers what has to be inside it. The demonstration is sitting in plain sight: Razer Huntsman Mini is published as a 60% board with 61 keys, and NuPhy Air60 V2 is published as a 60% board with 64. Same label, three keys of difference, and the difference is not decorative.

The extra keys on a slightly wider board tend to be arrows, or a column of navigation keys down the right edge, and those are exactly the keys a strict 60% makes you reach through a modifier for. So the number you actually want on the product page is the key count, not the percentage, and the second number you want is what the vendor says is in that count.

Only some manufacturers publish a key count. The table below is built from the boards that do. Where a manufacturer does not publish one we record nothing rather than counting keys in a product photograph, and a missing figure in that table means exactly that.

A layer is the whole keyboard reinterpreted while you hold one key down. Shift is the layer everybody already understands: hold it and the entire board means something else. Fn works the same way, and on a board with no function row it is what turns the number row into F1 through F12 for as long as your thumb is on it.

That is the trick that makes small boards workable at all, and it scales further than most people realise. Firmware can define several layers, so one board can carry a function row, a navigation cluster and a number pad stacked on top of each other, each reached by a different modifier. Nothing is missing in the sense of being gone. It is one press further away.

How much control you get over that arrangement depends on the firmware, and boards fall into three groups. Some run QMK and VIA, which are open firmware and a graphical editor for it, and let you put any key anywhere on any layer without writing code. Some run a manufacturer's own application instead, where remapping exists but stays inside what the vendor chose to expose. The rest offer nothing at all, and on those the layout is a physical fact you live with.

If you are considering a small board, this is the feature that decides whether the compromise is bearable. A 60% you can remap is a board with your keys in unfamiliar places. A 60% you cannot remap is a board with somebody else's opinions in unfamiliar places.

Three things have to line up, and CORSAIR states them in the same order on its own compatibility page: a standard bottom row, MX-stem switches, and MX-stem stabilisers under the big keys. Miss any one and the set will be partly unusable rather than slightly wrong.

Keycap widths are measured in units, written u, where 1u is one letter key. MonsGeek's compatibility guide gives the convention most full-size and tenkeyless boards follow: modifiers along the bottom row at 1.25u with a 6.25u spacebar. Depart from that and you have a non-standard bottom row, which usually means a wider spacebar, some boards use 7u, or modifiers at sizes a normal set does not include.

Compact and squeezed layouts are where this bites. MonsGeek notes that 65% and 75% boards commonly need a 1.75u right Shift, and that the 1800-compact family needs its own number pad keys and odd 1u and 1.5u modifiers, which is why sets aimed at those layouts ship what vendors call a compatibility kit. So the general shape of the rule is unkind: the smaller and cleverer the layout, the more likely a keycap set will leave you with four keys you cannot replace.

Start with the switch stem: an MX-compatible keycap needs a compatible MX-style stem. Then check key sizes, stabilisers and clearance. Low-profile keyboards need particular care because switch and keycap compatibility varies by design. Do not assume caps are interchangeable on a scissor or membrane keyboard.

Start from the blocks rather than the percentage. Decide whether you enter numbers often enough to want the pad, then whether you use F keys often enough to want them under a finger rather than under a modifier. Those two answers pick your size, and everything below that is packing.

Then read the key count and, if you can find it, the standard. A board that publishes 84 keys and calls itself ANSI 75% has told you what you are getting. A board that says 75% and nothing else has told you a price bracket.

For the board-by-board version of this, with our own size tag defined by what is physically present rather than by a percentage, read Full-size, TKL or compact: which keyboard size should you get? And if you want to see these keyboards alongside the mice and headphones instead of on their own, the setup builder puts all three columns together.