Edit: Wikipedia gives the following requirements for "unit of account":
To function as a 'unit of account', whatever is being used as money must be:
Divisible into smaller units without loss of value; precious metals can be coined from bars, or melted down into bars again.
Fungible: that is, one unit or piece must be perceived as equivalent to any other, which is why diamonds, works of art or real estate are not suitable as money.
A specific weight, or measure, or size to be verifiably countable. For instance, coins are often milled with a reeded edge, so that any removal of material from the coin (lowering its commodity value) will be easy to detect.
Except for having a specific weight, Bitcoin has these: 1 Bitcoin is the same as any other, and it can be broken into 0.5, 0.1 and even 0.0001 Bitcoins.