If your Acer has been in the ground for longer than 3 years, don't try moving it. If it was autumn or winter, it'd be worth a shot,but this time of year, no, it'll most likely just die.
In terms of the rootball, its hard to predict, particularly after a couple of years - roots spread where they have to to find water, and that may be deep down into the ground, or a long way along the surface, or both.

thanks

The roots do tend to be shallow and v shape - lots at the top, getting thicker and lesser the further down you go. If you really must move it (Bamboo is correct about that it prob will die - Acers are sulky things and prone to die off at best of times) then you need a wide pot. Are you able to come back and take it in autumn?

id leave it and buy another one realy .