That solely depends on what sort of hardware you're going to have it hooked up to and at what temperatures you're going to subject the PSU to operate it...much like how you calculate how fast a bottle will fill up with a certain fluid/liquid at a particular flow rate. Mathematics is going to be involved in this, not guess work.
You can't exactly classify mining a long term usage category, gaming or computing on the other hand can be deemed as long term tasks, as they are consistent. To give a nutshell advice, whatever you use to mine, they're going to end up in the e-waste pile faster than they would if you didn't mine with them. You need to also look into what you're looking to mine and see if it's feasible for you(and your region, India, as stated in your About).