As a freelancer, "hour worked" and "billable hour" are two very different things. If you're billing $x/hour, then you're earning much less when you count in all the hours that are work that's required for sustainable freelancing but aren't billable - finding clients, negotiating with them, making proposals for prospects that in the end don't become clients, handling your business/taxes/legal/advertising/etc.

Taxes/etc are a different issue on top of that, but a freelancer should expect to work many hours at a high rate, and many hours at the rate of $0/hour.