A number is not feasible. $10/hour in a small west Texas town is a handsome sum indeed. You can't park your car for $10 in San Francisco.
But ultimately, a wage is worth as much to an employer as will produce a sufficient profit for that employer. A person who does nothing but put pepperoni slices on a pizza on an assembly line or who picks up the trash at a construction site, and who is not qualified for anything other than that, will often be happy to get $5 or $6 in wages. Most such people live with others and do not have to fully support themselves and manage nicely on what to many of us would be pocket change.
But people will pay only so much for a crappy frozen pizza. Make that pizza more expensive than people are willing to pay, and the manufacturer will close down that product line. And then the assembly line worker no longer has a job at all.
Make the wage so high that the contractor will not take on the expense of an extra clean up or go-fer emplyee, and the contractor will just eliminate the job and have his regular crew spend a few minutes doing that work. And the entry-level employer is left high and dry.
A wage should be a contracted amount between the worker and an employer. In a free market system, the employer bids as much as he can afford to get the best people who will help his business prosper; the worker sells his labor to the highest bidder. But price the labor out of the free market range and the result will be many more people unemployed and on public assistance.
People who don't like being stuck in low wage jobs do what they have to do to make their labor more valuable. Meanwhile the bottom rungs of the labor pool are available for those who just want pocket change or who need an opportunity to acquire a work ethic, skills, references, and make themselves worth more money to an employer.
Instead of trying to fix low wages with a higher minimum wage, we do the people a far greater service with a healthy and thriving free market economy that produces full employment. That one thing makes the workers labor more valuable and worth more money.