If you were to die tomorrow, how much would you need to leave to take care of your obligations?
I feel compelled to clarify: How much would you need to leave in order to leave your DEPENDANTS clear of your obligations?
That is, how much do you need to ensure that the cosigners on your loans are not left shouldering your debt? And how much would it take to ensure that any children you have are taken care of?
DoingHomework implied that you should have enough life insurance to cover your debts. But that's not necessarily true. If you don't have any co-signers, you don't need life insurance to cover your debts. Your lenders already have insurance to cover those of you who die without paying back your debts, and the interest rate on your loans is designed to ensure that they make enough profit to cover those few of you who die before paying back the loan.
DO NOT BUY LIFE INSURANCE TO PROTECT YOUR LENDERS. Buy life insurance to protect your co-signers and dependants. Your lenders have already factored the risk of you dying into the interest rate. They will be fine.