how to calculate uncertainty of one value only.?

Question

how to calculate uncertainty of mass M=23.34g? one value only.

Answer 1

all depends on your measuring device and the thing your measuring.  I'd usually assume +/- 1 in the rightmost digit for balances. 

Answer 2

Supposing the given value was rounded off correctly:

23.34 ± 0.005 g

Answer 3

i dont need to calculate - i know.

I do not help people appear smarter than they actually are.