[lrasinen]

I usually go with 240 ml if scaling down and there are fractions involved for slightly cleaner numbers.

Another "close enough" value is the binary inch of 25.6 mm. Makes dealing with /32s and /64s oh so much easier.

[capitainenemo]

True. At that point you're close to the intent of teaspoons/tablespoons/cups with easier to remember units. tsp = 5ml tblsp = 15ml cup = 240ml

with all the handy halvings in between + higher granularity of ml.. 'course I'm usually approximating on a gramme scale anyway.

But for larger stuff I round up to 250.