Put in what's in your house right now. You'll get the number of days you'd make it, what runs out first, and exactly what it takes to reach 3, 14, 30 or 90 days.
The viral 90-day number comes from a Pentagon plan to keep military bases running off-grid. There's no announced threat to homes, and Ready.gov's baseline is a few days of supplies. Knowing your number is still smart, especially in hurricane country.