Fire extinguisher calculator
An office, classroom or assembly hall needs one 2-A fire extinguisher for every 3,000 square feet, on the figure OSHA publishes. This calculator applies that rule floor by floor and shows you the walk to check next.
This page is general information, not professional advice, and it is not legal advice. Fire code is adopted locally, and the count that governs your building is the one your own fire marshal signs off on after seeing the floor plan.
Now walk it: the travel-distance check
From any point in the building, how far is the walk to the nearest suitable extinguisher? Not the straight line — the walk, because NFPA is explicit that occupants are not expected to walk through walls. These are the published limits.
| Hazard | Maximum walk | Where it applies |
|---|---|---|
| Class A — ordinary combustibles | 75 feet | Everywhere employees work |
| Class B — flammable liquids | 50 feet | Workshops, storage, garages, warehouses, service and manufacturing areas |
| Class K — cooking oils and fats | 30 feet | Commercial kitchens |
| Class D — combustible metals | 75 feet | Measured from the hazard itself, not from the room |
On a large open floor, NFPA publishes 106 feet as the practical spacing between Class A extinguishers. Spacing them 150 feet apart satisfies the 75-foot rule in a straight line and leaves the corners of a rectangular room out of reach.
Figures last read from their sources on August 23, 2026.
Where every figure on this page comes from
OSHA, 29 CFR 1910.157 supplies the travel distances for Class A and Class B hazards and the duty that sits on the employer. OSHA Evacuation Plans eTool supplies the 3,000 square feet per 2-A unit for light-hazard spaces, attributed there to NFPA 10 Table 6.2.1.1, along with the 30-foot Class K limit and the 75-foot Class D limit. NFPA supplies the 11,250 square foot ceiling, the 9,000 square foot worked example for a 6-A unit in an ordinary hazard occupancy, and the 106-foot practical spacing. Each was read first-hand on the date stamped above.
Why there are three coverage figures and not a slider
Because NFPA 10 sets the maximum floor area per extinguisher from a table, and that table lives inside the standard rather than on a page anyone can read. Three figures out of it are published in words on pages we can cite, so those three are the ones offered. A slider running smoothly between them would look more useful and would be our invention. On a price page an invented number costs somebody money; on this page it costs something else, so the rule is applied harder here rather than more loosely.
The rule the calculator cannot see
Travel distance is measured as the walk, and NFPA is explicit that occupants are not expected to walk through walls. A tool that knows your square footage and nothing about your floor plan cannot check that, which is why the distances are printed rather than computed. It is also the reason buildings drift out of compliance quietly: put up a partition during a fit-out, lock a connecting door or stack pallets across an aisle, and the walk changes even though nothing came off the wall.
The deeper pages behind this tool: what a fire extinguisher inspection costs, the fire classes and what the label means and what a fire protection company actually does.
Questions people ask about this
- How many fire extinguishers do I need per square foot?
- For light-hazard Class A spaces — offices, classrooms, assembly halls — OSHA's eTool publishes NFPA's recommendation of one 2-A extinguisher for every 3,000 square feet. Larger coverage figures apply to higher-rated units, up to NFPA's ceiling of 11,250 square feet for a single Class A extinguisher.
- Why does the calculator only offer three coverage figures?
- Because those are the three a primary source states in words we can read: OSHA's 3,000 square feet per 2-A unit, NFPA's worked example of 9,000 square feet for a 6-A unit in an ordinary hazard occupancy, and NFPA's 11,250 square foot ceiling. NFPA 10's full table sits inside the standard, and inventing a row between the published figures would be inventing code.
- Does this replace the travel-distance rule?
- No, and neither replaces the other. NFPA 10 applies a maximum travel distance and a maximum floor area at the same time, and the more restrictive of the two governs. This tool computes the floor-area side and prints the travel distances for you to walk.
- How far apart should fire extinguishers be?
- NFPA publishes 106 feet as the practical spacing on an open floor. Spacing them 150 feet apart satisfies the 75-foot rule in a straight line, but because rooms are rectangles it leaves corners further than 75 feet from an extinguisher.
- Is this number what my fire marshal will accept?
- It is the figure to walk in with, not a verdict. Fire code is adopted locally, your insurer may ask for more, and partitions, locked doors and stacked stock all change the walk. The count that governs your building is the one your fire marshal signs off on.
Keep reading
What things cost
Common questions