[nostrademons]

You want enough that you have a reasonable chance of making adaptations in your lifestyle if you lost your job. "Adaptations" includes finding a new job, downsizing to a smaller home or apartment, or moving to a new metropolitan area.

3 months is taking a pretty big risk. If you're in your mid-20s, you've never lived through a recession. It is possible to lose your job concurrently with the stock market losing 50% of its value concurrently with nobody in your industry hiring for 6-12 months (indeed, that number is often picked so that you can ride out the worst of a recession). If you have other assets and no debt, you at least won't be penniless and on the street, but you can be forced to sell stocks & mutual funds at fire-sale prices and wipe out much of your net worth if a downturn happens. Or you may end up having to take a job that sets you back a couple years in career progression rather than being able to wait for the right opportunity to come around.