what do inmates need money for?

Depending on where your inmate is incarcerated, they will have a weekly or monthly spending limit. Most county jails have a $50-75 per week limit. Federal has a $340 per month spending limit. There are also the cost of the phone calls to be considered. You should budget according to your own needs first and then the inmate's. Some people on the outside worry about their inmate so much on the inside that they send them more money than they can afford and it weighs down their own ability to survive. Don't get too caught up in your inmate saying "they need a certain amount of commissary money" because the jail provides everything that they need to get through their time - commissary just offers a bit more "comfort".