Classes A fires relate to homes and households, and are among the most common. They involve "ordinary" combustibles such as wooden furniture, paper trash, clothing and curtains, and ever the kind of rubber found in your shoes.
Unlike in Europe and Australia, all flammable liquids and gases
are classed as Class B in the United States. These kinds of liquids are usually found in your garage, workshop and kitchen.
Class C relates to electrical fires and electrical equipment.
In relation to Class A, you multiply the number in front of the letter by 1.25 to to give you how much water
the extinguisher contains. For example, a Rating of 2-A shows the unit contains 2.5 gallons of water.
For a Class B Rating, the number shows how many square feet the extinguisher can suppress.
Classes C, D, and K do not have a numerical rating.
So, to take the Kidde Pro immediately below as an example, this is an extinguisher with a 2-A:10-B:C Rating. This translates to it containing 2.5 gallons of water, that it can suppress fire over 10 square feet, and is suitable for fighting fires in the A, B, and C categories, as described above.
We have written more
about fire suppression, the different types of fire extinguishers, and the Classes of fire.