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Type A and B fire extinguishers have numbers next to them to show how much capacity they have to put out fires. A number next to an A on a fire extinguisher relates the contents of the extinguisher to an equivalent amount of water. Each number equals 1.25 gallons of water. So a “1” next to the A means the extinguisher has the equivalent of 1.25 gallons of water, a “2” equals 2.5 gallons and so on. Numbers with the letter B refer to how many square feet of fire the extinguisher can put out. So 4B means the fire extinguisher can douse a 4-square-foot fire caused by flammable liquids. Class C extinguishers do not have any numbers associated with them.

Many home fire extinguishers are rated to put out more than one kind of fire. You might find an extinguisher labeled 2A10BC. This extinguisher contains the equivalent of 2.5 gallons of water, can put out about 10 square feet of flammable liquid fire, and can extinguish electrical fires.

The larger the number of the fire extinguisher, the larger the area of fire you could put out. But bigger fire extinguishers are often heavy and take up a lot of space, making them inconvenient for most homes. Plus, it’s dangerous to try to put out a large fire yourself. Instead of one very large fire extinguisher, consider keeping several smaller fire extinguishers in your home.