This essay summarizes my process of designing an “optimal” keyboard layout. You can view the layout layer by layer at QMK configurator by uploading one of the JSON files. If you are just interested in the finished layout, feel free to skip to The final layout.

• Why 40%
• Motivation
• Reducing capitalization to one key
• The power of QMK
• Numbers without a number row
• Special characters
• Making the keyboard complete
• The final layout

When I was searching for a new keyboard back in 2019 I realised that I was looking for the smallest possible, yet efficient, keyboard. I wanted an ortholinear keyboard since it minimizes the keyboard footprint, but you can argue that keyboard size is more accurately defined by the number of keys. Anyways, I concluded that a 40%, more specifically a 4x12, is the smallest keyboard that meets the following requirements:

• QWERTY on a 3x10 grid
• ESC and TAB on the left
• Backspace on the right
• The CTRL, Super, Alt and Spacebar on the bottom

The purpose of the layout is to combine a small footprint with an efficient layout. A 4x12 footprint means that the fingers can stay on the home row. This is intrinsically efficient but has to be combined with a sensible layout that doesn’t restrict typing speed or usability.

I think anyone coming from a keyboard with 68 keys or more would naturally place Right and Left Shift under TAB and apostrophe ('), and Capslock somewhere on the bottom row. I think that having three keys for capitalization is ludicrous. In addition to the fact that when your “home row pinkies” press Shift, like in the image below, you can no longer press Q, A, Z, or P with their dedicated fingers. One could argue that this quirk of Shift placement doesn’t necessarily affect typing speed, but I fundamentally dislike it and believe that capitalization should be done differently.

Why two Shift keys in the first place? I’d argue that it stems from the capitalization problem of A, Q, Z, and P. This is (I guess) also the reason why we have Caps Lock, since holding down Right or Left Shift permanently isn't feasible.

Okay, so how do we improve this? The reason for multiple Shift keys is that the home row pinkies can’t be held down permanently, this is what creates the need for Caps Lock. That means that if we solve Shift keys we don’t need Caps Lock. And the problem with Shift keys is that their fingers, the pinkies, are needed for other important keys. In fact, it doesn’t make sense to use any of the home row fingers for capitalization, because they press the letters to capitalize. That’s why using the non-Spacebar-thumb for Shift magically reduces capitalization to one key, since it can be held down permanently.

At this point it might seem like the layout is running out of keys, yes, but actually no. QMK is a powerful keyboard firmware tool that allows for arbitrary layers. If you have every used the FN-key this concept is familiar. But doing this for any type if key allows for complex and powerful keyboard layouts. I'd recommend checking out all the built in features at QMK config.

IMHO the numpad is just superior. It felt very natural to place the numbers on a dedicated layer. Simply press "left shift" to change the keys under the right hand to a numpad. They ended up on the right "under" the home row. This is both convenient and fast since the fingers doesn't have to move.

Special characters are usually mapped to the number row, so it's natural to dedicate a new layer. They can be placed on the same layers as the numbers, but this is unintuitive and unnecesassry. As you can see in the image below most of the special characters are where they would be on a QWERTY layout. But since the keyboard is only 12 keys wide I had to make some adjustments.

• Prioritized (~)-($), deprioritized (%), (^) and (&)
• Mapped (-) and (=) to my dominant finger (right index)
• Mapped paranthesis' to the middle home row fingers

This is surprisingly easy to adapt to and I actually prefer this parenthesis-layout over QWERTY's.

Other small keyboard usually have the arrow keys in the bottom right corner. This keyboard footprint doesn't allow for that, but I don't mind since we can do better. Just like with numbers, they just magically appear under the right hand when we press "right shift". Clean and efficient. Function keys are placed on the left side of this almost empty layer.

To finish up the layout i use some more QMK features which result in the following:

• The "escape key" is normally ESC, but now (~) when shift is pressed
• The Shift and Enter keys from before are combined into one: Enter when pressed, Shift when held down
• The Del key is now on the bottom right
• Layer 1 is updated
• Layer 4 is new

In addition to numbers this layer now has Media keys, a Power key, a Reset key and RGB control.

This layers allows for cursor control without a mouse.

• Update images to be consistent with new keys added