I provide support for my uncle, how much would another adult (he is 56) qualify for on my taxes? I need to know if it is even worth it to list him as my dependent.

Each dependent that you claim reduces your taxable income by $3,650. The amount this is worth to you is dependent on your tax bracket - for example if you are in the 15% bracket then an additional dependent will save you $3650 * 15% = $547.50 on your taxes.

By the way, in order to claim your uncle as your dependent he must have lived with you in your home for the entire year, his income must be less than $3,650, and you must have provided at least half his support during the year.