I’d recommend anyone interested in 40% layouts to get a qmk powered 60%. You can setup a layout that only uses the 40% area and play with different keymaps. That will allow you to try 40% without committing. Worst case scenario you just reprogram as a 60% or sell on r/mm.
I have a couple 60% keyboards programmed very similarly to my MiniVans and love em
Hey that’s a nice idea, do you have the key maps available somewhere for inspiration?
I own an Iris and an Ergodox. To me the Iris is big enough for all my use cases (emails, some programming, a bit of gaming).
I think an Iris with on row less (would be 40%), would still work well, except probably for gaming.
So my conclusion is that a 40% with a thumb cluster is good enough for almost all uses cases.
Why would you want a smaller keyboard?
My assumption is that you really do not want to look at the keyboard when typing, navigating (curso keys), etc and special keys (F keys, volume etc).
Practically that means that ideally you want 3 rows (40%) or at max 4 (iris). More rows are just not easily reachable with looking down to the keyboard. You can use a few layers to cover all the keys.
I can upload my 60 setup later today
I mostly use my 40% keyboards when travelling. The size makes them perfect for that.
I am coming from ISO layout so I usually have 3 layers
layer 1 = alphas + default punctuation
layer 2 = numbers on upper row and a few special characters in the home-row (+ arrow keys in some of my layouts)
layer 3 = what equals to alt-gr+number in the upper row. F keys in the lower row.
This gives me everything I need as a developer and the finger-travel equals the one I have from my other “normal” keyboards in terms of direction and placement (going for number row /altgr+numbers feels “normal”).
Why are they F keys so different?
There are several ways to make them easily reachable with qmk. You could for example put the layer key on one side as well as the modifiers and the f Keys in the other half of the keyboard.
Personally, I’m of the opinion that 40% boards appeal to the same type of person that loves fiddling with their graphic sliders and driver settings on their computer games, marvels at the beauty, takes screenshots, posts them, then shuts off the game.
I respect that, to some, that is the game.
To me though, my board is in service to my use. I require that all the keys my fingers know, be there in the place where they should be. And that includes the num row. So, no lower than a 60%. I’m not about to retrain my brain for a marginally more compact footprint.
I will admit that I never thought I’d go lower than a TKL and now I’m happy as a clam on a 60%, so I’m probably just stubborn, biased, and crabby on the subject of 40%.
My son has a couple of 40s, and this is a topic of discussion between us. I just don’t get it, but I hear you all, and you’re cool.
Are you saying size matters?
This thread has me thinking I’d want to try a layout without a number row, but with a number pad on the right. There are few things I hate more than typing digits on the num row, and I’m fast and accurate af on the num pad due to early training entering massive amounts of numbers. I also love having an enter key in the bottom right-hand corner to MASH without having to aim, which I do embarrassingly often out of frustration after entering the wrong password too many times.
The top alphas or the numpad could double as the standard ! @ # $ etc.
Hmmm…
Whats harder to type on a 40%, mandarin, cantonese, or english?
I mostly agree. I’m also not yet at 40%. I love my Iris, it’s more like a 50% board.
But in principle I think it is not that difficult to get rid of the number row.
Either learn how to type numbers on a numpad and put that numpad on some layer.
Or just put the numbers on a separate layer, but for example on the home row or the top row on the smaller keyboard. Mentally it is relatively easy to learn that, the row is just closer than is used to be.
I think most people need to go through a similar downgrade where they learn how to live with a couple less keys at a time. Maybe we need some keyboard renting service designed to help people try out new keyboards. Just make sure to use pbt keycaps and clean every board that comes back.
BTW it is a little bit more than 40%
but this
Looks to me like the sweetspot for most uses cases. I think one could make it smaller (closer to 40%) and it would be still enough for a lot of use cases.
Type Chinese (no matter mandarin or cantonese) are a bit more complex than type English, because we need use number choose the Chinese characters when we type the uncommon word.
40% is insufficient for any indo-european language (except english), let alone mandarin and other complex Asian languages.
There is no way you cram German (or any other ISO) layout on such board withot using second layer.
It’s possible to fit all German alphas (and other ISO languages) on a Planck if you’re willing to get rid of some of the mods on the right hand side. But a Planck has some more keys than a “true 40%”, so that might be cheating 
I mean, you can’t cram ansi onto a 40% keyboard without using a second layer, so I don’t understand your point.
You could have all alphas and punctuations (those important ones), and this is what matters in daily life.
But, if I have to press F key five times just to finish one regular sentence, than you start to realize 40% layout is basically useless.
Well you press the shift key upwards of 5 times in many sentences, so maybe its not as bad as you think. Maybe you’d just need to find a more comfortable position for the layer key.
With Japanese rōmaji input, you pretty much just need the alpha keys and a ‘convert’ key, which is often the spacebar. I guess you’d also need a key to input the long vowel marker for foreign words rendered in katakana, too, and then a few punctuation keys would be convenient.
In any case, a 40% might be pretty effective for Japanese, perhaps even more so than for English. 
edited to add: I have no experience with typing in Korean, but it looks like the standard layout has all the hangeul on the alpha keys. Maybe Korean would work on a 40% just fine, too. I’m sure someone on Keebtalk with actual Korean knowledge can chime in 