How Much Do I Need to Retire in Comfort?

If you do a quick Google search, there are a lot of results claiming that you need a specific amount of money in order to retire comfortably. However, everyone is different and have varying needs. Kim Kardashian will have different expectations than your average Kiwi, so her retirement fund needs are probably higher than most peoples. So how can you figure out what you will need? What do you need to take into account?