Numbers on Class A & B extinguishers represent capacity.
The number before the “A” (ie. 1-A) represents the gallon capacity of water or other extinguishing agent x (times) 1.25
1-A = 1.25 gallons
2-A = 2.50 gallons
5-A = 6.25 gallons
Class A extinguishers are rated between 1-A & 40-A
Class B extinguisher ratings are based on square footage.
A 10B rating would allow the extinguisher to control a fire of 10 square feet.
5B = 5 square feet
60B = 60 square feet
Class B extinguishers are rated between 1-B & 640-B
Class C & Class D – Do not carry a numerical rating.