I am looking to buy new units for my very narrow kitchen. I am having trouble understanding depth sizes. My current unit depth is 400mm, looking at units and sinks online and noting the "Minimum cabinet size" I see that many sinks that are 500mm wide say minimum cabinet size 450mm. I assume then that I would need a counter top of at least 500mm to fit the top of the sink properly but it would then overhang the cabinet unless I have the unit away from the wall. Is that right or am I getting my measurements confused. Is all I need to do find a sink that's less than 400mm width. ?
Correct on both counts, find the smallest depth sink that would suit the area and work from there. If you are really tight on space you can mount wall units on legs which I think are 320mm deep from memory, but you aren’t going to get a sink to fit that obviously. Edit, I’m incorrect and Mark above is very much correct.
Depth is front to back, width is side to side. Base units depths are typically around 580mm, and countertops usually come in at 600mm. (you can of get shallow base units, but they're not standard sizing)
The reason minimum cabinet size is quoted is because the sink bowl needs to sit inside the cabinet even though the sink itself may be considerably wider especially if it has a drainer. In these circumstances the drainer would extend over an adjacent cabinet or appliance.