Questioning the ergonomics of 40% keyboards
Pascal Getreuer, 2022-04-26
Small 40% keyboards of approximately 40 keys have a lot of attention around the custom keyboard community. Noting low finger travel, it’s commonly suggested that 40% keyboards are ergonomically beneficial. This is questionable advice for people looking to improve their typing comfort. While smaller keyboards do reduce finger travel, they make other things worse. On the whole, 40% keyboards are not a clear win.
To be clear, I’m not saying 40% keyboards aren’t practical. People can and do use them practically. If you use a 40% or below and enjoy doing it, don’t let me stop you.
However, if your interest in custom keyboards is ergonomics, as it is for me, then 40% keyboards are a questionable direction.
The ergonomics argument for 40% keyboards is that “all keys are at most 1u away from home row position, so finger travel is lower than it would be on larger keyboards.” This is good. The compromise made though, with so few keys, is that extensive use of layers, combos, or other tricks is unavoidable to represent frequently used keys. That means a lot more key presses and stress on the hands (to change the layer, to make the combo, …) to accomplish the same typing.
More key presses = more work, counteracting the benefit of lower finger travel.
Combos are more work than regular keys. For instance, combo’ing on 3 keys needs 3x actuation force compared to a single key. Combos are sometimes advocated noting that this resembles how stenographers make strokes on only 22 keys. But to make this ergonomic, stenotype machines use switches with under 10 gf actuation force, well below the typical 40–60 gf actuation force on keyboards.
Layers make it possible to put more keys on or near home row, which is good. But there is a tradeoff that switching layers in itself costs pressing and holding a key (or tapping a key, depending on the type of layer key), and on its own, pressing a layer switch accomplishes no typing. Layers become inefficient when switching is frequently needed. While a well-designed keymap mitigates switching by placing co-occurring keys on the same layer, a 40% keyboard has limited space per layer, and frequent layer switching is inevitable.
The base layer gets much better even with just a handful more keys. For instance 56 keys is enough to fit a traditional layout alphas area (30 keys), number row (10 keys), and outer columns (8 keys) on the base layer plus a few more keys (8 keys) on the thumbs or bottom row. This isn’t necessarily optimal, but likely closer to the sweet spot between low finger travel vs. avoiding layers and combos for frequent keys.
See also: PSA: Thumbs can get overuse injuries