How the fire extinguisher calculator works
This fire extinguisher calculator follows NFPA 10, the national standard for portable fire extinguishers. It starts with your occupancy hazard, then checks two limits. One limit is the area one unit may cover. The other is the longest walk to the nearest unit.
The tool takes the stricter result and rounds up. It also adds Class B, Class K, and Class D units when your building has those hazards. You get a unit count per floor and a total for the site.
Think of it as a first pass. A fire marshal or licensed Texas service company will still walk the building. They look at walls, racks, doors, and real walking paths. Those details can add units.
Light, ordinary, and extra hazard occupancies
NFPA 10 sorts every space into one of three hazard levels. The level depends on how much fuel is there and how fast a fire could grow. Higher hazard means more extinguisher capacity.
| Hazard | Typical Texas spaces | Minimum Class A rating |
|---|---|---|
| Light | Offices, churches, schools, hotel rooms | 2-A |
| Ordinary | Retail stores, restaurants dining areas, parking garages, light manufacturing | 2-A |
| Extra | Woodworking shops, auto repair bays, warehouses with high-piled stock, flammable liquid handling | 4-A |
When a building mixes uses, treat each area by its own hazard. A warehouse with a small office is mostly an ordinary or extra hazard. The office can be treated as light.
Class A area limits by rating
Class A covers wood, paper, cloth, and trash. The table shows how much floor one extinguisher may protect. Each A in the rating earns a set number of square feet, and the cap is 11,250 square feet per unit.
| Rating | Light hazard | Ordinary hazard | Extra hazard |
|---|---|---|---|
| 2-A | 6,000 sq ft | 3,000 sq ft | Not allowed |
| 3-A | 9,000 sq ft | 4,500 sq ft | Not allowed |
| 4-A | 11,250 sq ft | 6,000 sq ft | 4,000 sq ft |
| 6-A | 11,250 sq ft | 9,000 sq ft | 6,000 sq ft |
| 10-A | 11,250 sq ft | 11,250 sq ft | 10,000 sq ft |
A bigger rating means fewer units, but each one weighs more. A 10-A unit is heavy for many workers. Some owners buy more 4-A units instead, so staff can lift them with ease.
Why 75 feet of travel distance matters
Travel distance is the walking path from any point in the room to the nearest extinguisher. For Class A fires, NFPA 10 sets the limit at 75 feet. Picture a circle with a 75 foot radius. The biggest square that fits inside has an area of about 11,250 square feet. That is where the per-unit cap comes from.
Straight-line distance does not count. You must measure the path a person would walk. A wall, a rack row, or a locked door makes the path longer. Because of this, a long, narrow building often needs more units than the math suggests.
Class B, C, D, and K rules
Many Texas businesses face more than one fire type. Each type has its own rule.
| Class | What burns | Max travel distance | Common agent |
|---|---|---|---|
| A | Wood, paper, cloth | 75 ft | Water, ABC dry chemical |
| B | Gasoline, oil, solvents | 30 ft or 50 ft by rating | ABC or BC dry chemical, CO2 |
| C | Energized electrical gear | Same as the A or B hazard nearby | ABC dry chemical, CO2 |
| D | Magnesium, titanium, sodium | 75 ft | Metal-specific powder |
| K | Cooking oils and fats | 30 ft | Wet chemical |
For Class B, the minimum rating depends on both hazard and distance. In an ordinary hazard area, a 10-B unit works at 30 feet and a 20-B unit works at 50 feet. Extra hazard areas need 40-B at 30 feet and 80-B at 50 feet. Light hazard areas need 5-B and 10-B.
Commercial kitchens need a Class K unit within 30 feet of the fryers and grills. Read our guide on Class K extinguishers for Texas restaurants for the full picture.
Mounting height and clearance
A unit nobody can reach does not help. NFPA 10 limits mounting height by weight. If the extinguisher weighs 40 pounds or less, the top must sit no higher than 5 feet above the floor. Heavier units must sit no higher than 3.5 feet. The bottom of any unit stays at least 4 inches off the floor.
Place units along normal exit routes. Keep them in plain view. If a rack or door hides one, add a sign that people can read from 50 feet away.
Worked example for a Texas warehouse
Say you run a 20,000 square foot distribution warehouse in Fort Worth. The space is a single floor and counts as ordinary hazard. You plan to buy 4-A:60-B:C units.
- One 4-A unit covers 1,500 x 4 = 6,000 square feet.
- Divide 20,000 by 6,000. The result is 3.33, so round up to 4 units.
- Check travel distance. 20,000 divided by 11,250 is 1.78, which rounds to 2. The rating limit is stricter.
- Your starting count is 4 units for general fire protection.
Switching to 10-A units changes the math. One unit then covers 11,250 square feet, so you need 2. The rating no longer controls the count, and the 75 foot walking limit does. Your inspector may still ask for more where racks block the path.
Texas rules, inspections, and who enforces them
In Texas, the local fire marshal acts as the authority having jurisdiction for most buildings. Many cities adopt the International Fire Code, which points to NFPA 10 for portable extinguishers. The State Fire Marshal's Office licenses the companies that service extinguishers.
NFPA 10 also sets a care schedule. Check each unit visually every month. Have a licensed technician service each unit at least once a year. Stored-pressure dry chemical units need an internal exam every six years and a hydrostatic test every 12 years. CO2 and water-based units need a hydrostatic test every five years.
Need help with any of this? Browse fire extinguisher inspection providers in Texas or compare sales options near you.
Frequently asked questions
How many fire extinguishers do I need for 5,000 square feet?
In a light or ordinary hazard area with 4-A units, one unit covers at least 6,000 square feet. So one unit meets the area rule. You still need one within 75 feet of every spot, and at least one per floor. A long or divided space often needs two.
What is the difference between 2-A and 4-A?
The number shows fire-fighting power. A 4-A unit holds roughly twice the capacity of a 2-A unit. That lets one 4-A cover double the floor area in the same hazard class.
Do I need a fire extinguisher in every room?
Not always. NFPA 10 sets distance and area limits, not a per-room rule. Closed rooms, though, block the walking path. Most fire marshals expect units in or right outside rooms that people occupy.
Can I use one ABC extinguisher for a kitchen?
No. Commercial cooking with oils and fats calls for a Class K or wet chemical unit. An ABC unit does not cool grease well enough to stop re-ignition.
How often must Texas businesses service extinguishers?
Inspect them monthly and have them serviced each year by a licensed company. Longer-term tests apply too, such as the six-year exam and 12-year hydrostatic test for stored-pressure dry chemical units.
Does this calculator replace a fire marshal inspection?
No. It gives a planning count. Your fire marshal or a licensed service company confirms the final number based on the real floor plan.
Related Texas fire safety guides
- Which fire extinguisher for which fire
- Texas NFPA 10 compliance guide
- Commercial fire extinguisher requirements
- Fire extinguisher maintenance guide
- PASS technique
Sources and standards
These references shaped the numbers and rules on this page. Always read the edition your local fire marshal has adopted.
- NFPA 10, Standard for Portable Fire Extinguishers
- OSHA 29 CFR 1910.157, Portable fire extinguishers
- Texas Department of Insurance, State Fire Marshal's Office
Last reviewed October 13, 2026.