World unit in real world metric

I’m interested how a “world unit” in jmonkeyengine translates into real world measures. For instance, if I place an object “1 world unit” away on the Z axis from the centre of the map, how many millimetres away is it?

Is there a conversion formula for this?

That is like asking how many meters does a pixel represent. It is your application that interprets what 1 world unit means. I can make a game with bacteria and decide that each cell is 100 world units large. Or I can make a space simulator and decide that 1 world unit is 1 light year.

If you are talking about bullet physics it is 1 meter.