Look at the extinguisher to the right. The classification is:
The letters (A, B, and C) represent the type(s) of fire for which the extinguisher has been approved.
The number in front of the A rating indicates how much water the extinguisher is equal to and represents 1.25 gallons of water for every unit of one. For example, a 4-A rated extinguisher would be equal to five (4 x 1.25) gallons of water.
The number in front of the B rating represents the area in square feet of a class B fire that a non-expert user should be able to extinguish. Using the above example, a non-expert user should be able to put out a flammable liquid fire that is as large as 10 square feet.
Please click here for more information on each type of fire extinguisher.