How many gallons do I actually need?

For car interiors and small spills, 2.5 to 4 gallons is enough and far easier to store and carry. For garage and household projects, 5 to 6 gallons is the sweet spot most reviewers recommend. For renovation work, drywall dust, or flooded basements, 12 to 16 gallons is worth the bulk because you empty far less often.