A form factor is the physical size and shape of a keyboard. A layout is the placement and size of the keys.
The most common form factors include:
Common layouts include:
60% - The main layer is the alpha numeric cluster. There is no numpad and the f row/navigation keys are accessed via layers under the main layer.
65% - This is a 60% with arrows and extra navigation keys on the main layer. Just like a 60%, the remaining keys are accessed via layers.
75% - The main layer includes the alpha numeric cluster, navigation keys, and f row. This form factor is basically a TKL(tenkeyless) in a condensed form factor.
80%/TKL/Tenkeyless - Like the 75%, a TKL includes the alpha numeric cluster, navigation keys, and f row but in a more standard layout. This form factor is a full size without a numpad.
1UP store link: DIY TKL
Full-size - The most recognizable form factor. A full-size form factor includes all keys on the main layer.
1UP store link: DIY Full-size
40% - Due to the nature of its size, a 40% form factor can include varying keys in the main layer. Most common will include the alpha cluster(no numbers) and various mod keys.
1UP store link: DIY 40
Ergo - Form factor aimed at ergonomic comfort. Note this is just one example of many.
Different layouts can be used on 60%, 65%, 75%, TKL, and full-size keyboards. It is important to understand key units when venturing into different layouts to ensure your key sets have proper coverage Key Units. Please note that many pcbs support various combinations of these layouts so use this as a reference to key placement and size.
Standard ANSI - 6.25u spacebar, 1.25u bottom row, full-size right shift.
Tsangan - 7u spacebar, 1.5u & 1u bottom row, split backspace, split shift.
HHKB - 7u spacebar, 1.5u & 1u bottom row with blockers, split backspace, split shift.
WKL (winkeyless) - 7u spacebar, 1.5u bottom row with blockers where 1u key(winkey) would reside.
Standard ISO - Used by many European countries with one extra key compared to ANSI keyboard
Ortholinear (olk) - Rows are straight and in line with each other.
Condensed 1800 - Condensed version of 1800 form factor.
96key - 1800 form factor condensed into one continuous layout.