Fire Extinguisher Numbers Explained

Along with smoke alarms, fire extinguishers are essential equipment for keeping your home and family safe from fires. Fire extinguishers in your house, garage, car and camper can help you put out small fires quickly, before they spread. But determining the right fire extinguisher to buy for your home can be confusing. When you go to the store you'll probably see many different sizes and types of extinguishers, with an array of different letters and numbers on the label. Understanding those numbers and letters can help you make the right decision about which extinguisher to purchase.

Fire extinguishers are rated for different types of fires.

Letter Ratings

In order to determine what the numbers on your fire extinguisher mean, you first have to interpret the letters that go with the numbers. Fire extinguishers are given letter ratings according to the type of fire they'll put out. Type A extinguishers put out ordinary fires of combustible material such as cloth or wood. You'll often see a pictogram of a campfire next to the letter A. Think A for ashes, since these types of material leave ashes when they burn. B extinguishers put out fires caused by flammable liquids such as gasoline, solvents and grease. These are items that can be sold in barrels, so think B for barrel. C extinguishers will put out electrical fires. Think C for current. Most home fire extinguishers are labeled for A, B, C or all three. You'll sometimes see fire extinguishers labeled D. These can extinguish fires causes by burning metals such as magnesium. These are very dangerous fires you shouldn't try to put out yourself. Think D for Don't touch.


A number next to an A on a fire extinguisher relates the contents of the extinguisher to an equivalent amount of water. The numeral 1 equals 1.25 gallons of water, the numeral 2 equals 2.5 gallons and so on. If you see the designation 3A it means the extinguisher will put out combustible material fires and the extinguisher contains the equivalent of 3.75 gallons of water. Numbers with the letter B refer to how many square feet of fire the extinguisher will put out. So 4B means the fire extinguisher will douse a 4 square ft. fire caused by flammable liquids. Class C extinguishers do not have any numbers associated with them.


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. Instead of one very large fire extinguisher you could use several small fire extinguishers. Most home fire extinguishers are rated to put out more than one kind of fire. So you might find an extinguisher labeled 2A10BC. This extinguisher contains the equivalent of 2.5 gallons of water and will put out about 10 square feet of flammable liquid, and it will extinguish electrical caused fires.

FIre Extinguisher Safety

Mount fire extinguishers within easy reach of areas of the home where you're most likely to experience a fire, such as the kitchen and the garage. Familiarize yourself with the extinguisher's operation. Most extinguishers require you to pull a pin or move a switch, aim at the fire and press a trigger. Don't try to fight a large fire on your own; leave the house and call emergency services. Fire extinguishers work best on small fires, such as a burning wastebasket or a small grease fire confined to a pan.