The fire extinguisher sizes are the numbers written alongside the fire extinguisher classification letters. This tells the size of the fire extinguisher.

Example, for the extinguisher classification – 2A:10B:C, the numbers in-front of the letters are the different sizes. It implies that the above fire extinguisher can put out a fire just as effectively as 2½ gallons of water since 1 equals 1¼ gallons of water; 10B indicates that you can expect to douse a fire that had spread to cover 10 square feet and a class C fire extinguishing agent.

Here are the different extinguisher sizes for different classes of the fire extinguisher:

• Class A extinguisher sizes: Class A size ratings range from 1 to 40. This tells you the water equivalency. 1 equals 1¼ gallons of water, so in this example, 2A means the extinguisher can put out a fire just as effectively as 2½ gallons of water.
• Class B extinguisher sizes: Class B size ratings range from 1 to 640. This number estimates the square footage an extinguisher can cover. In the above example, 10B indicates that you can expect to douse a fire that had spread to cover 10 square feet.
• Class C,D OR K extinguisher sizes: There are no numeric size ratings for fighting Class C, D, or K fires because these classifications simply indicate that the extinguisher is recommended for fighting electrical fires, flammable metal fires, or kitchen fires, respectively.

READ: P.A.S.S Fire Safety (How to Use Fire Extinguisher)

Here are some common sizes of the portable fire extinguisher:

Foam fire extinguisher 

3, 6 & 9 Litre

Water extinguisher

3, 6 & 9 Litre

Dry powder extinguisher

1, 2, 4, 6 & 9 Kg

Carbon Dioxide

2 & 5 Kg

Wet chemical extinguisher

3 & 6 Litre

READ: What Do The Symbols On A Fire Extinguisher Indicate

Aside from this portable fire extinguisher sizes, there are industrial sizes for fire extinguishers, like – 25kg CO2, 25kg & 50kg DCP, 50 Liters foam, 50 Liters Water.