How much electricity does the Volt use?

We don't have all of the information we might like. On the one hand, the 1st-generation Volt gets at least 40 all-electric miles on both the EPA city and highway cycles, and does it using an effective battery capacity of 8 KWHs (50% of the nominal 16 KWHs). That gives us .2 KWH/mile, battery to wheel.

Efficiency is likely to improve with later generations - especially aerodynamics (the most important factor with an electric drivetrain, where regenerative braking greatly reduces acceleration/braking losses), but also peripheral loads. The importance of aerodynamics can be seen with the ultra-streamlined Aptera, which is expected to use only .07 KWH per mile.

On the other hand, that doesn't include the charge-discharge losses, which are usually 7-10% for li-ion, or AC-DC conversion losses, which can range from 1% to 75% (for small, cheap "wall-warts"). And, those efficiency improvements could easily go to larger vehicle size (though not to acceleration: one of the nice things about electric motors is that they get more efficient as they get larger, unlike infernal combustion engines).

You could use .25KWH/mile, if you wanted to be conservative.