The expense replacement method is begun by figuring out the needs of the surviving family. Determine what bills are most important to be paid when you die. Add them together and that's how much graded life coverage you should buy
Because burial life is usually low benefit, you can only buy so much or it. If you are terminal and have the funds available, you may consider buying multiple policies.
Usually you want to buy enough to get the insured into the ground. Because the insured's heirs get a percentage of their money back if they die before the 2-5 year waiting period, there is little risk, unless that person lives for much longer.
The expense replacement method is my short answer.
My long answer is: Buy all you can afford to cover your bills when you are gone (if you have major health problems). You may have to buy multiple polices since most offer a maximum of $25,000. And lastly, get enough coverage to provide for your last wishes.