what size gap to leave for washing machine and dishwasher?

hi

i'm soon to start fitting a new kitchen, i've got a freestanding washing machine and dishwasher that will fit in under the worktop. and so i need to leave a gap for these. i need to leave the gap as tight as possible for space and aesthetics.

the washing machine is 599mm wide and the dishwasher 600mm wide. is there a standard size gap that should be left for appliances like this? i'm intending to get some of those appliance rollers to make it easier to get it and out. anyonme got...

what size gap to leave for washing machine and dishwasher?