Fire Extinguisher Coverage Calculator
Estimate how many portable fire extinguishers a floor area needs so that no one is ever further than the maximum allowed travel distance from a unit. It is a quick spacing check to inform, not replace, a proper fire-safety assessment.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the floor area to be protected in square metres.
- Optionally set the maximum travel distance to reach an extinguisher (default 15 m, a common Class A limit); use a shorter distance for higher-hazard areas.
- Read the number of extinguishers required and the coverage area each one provides.
How it works
Each extinguisher is treated as protecting a square whose half-diagonal equals the maximum travel distance, giving a coverage area of 2 × (travel distance)² per unit. The number required is the floor area divided by this coverage area, rounded up to the next whole extinguisher, with a minimum of one.
Worked example
Worked example. A 600 m² workshop with a 15 m travel limit: coverage per extinguisher = 2 × 15² = 450 m², so extinguishers required = ceil(600 ÷ 450) = 2. A larger 1200 m² area with a 20 m limit gives 2 × 20² = 800 m² per unit and ceil(1200 ÷ 800) = 2 extinguishers.
Common mistakes
- Applying the default 15 m travel distance to a high-hazard area — flammable-liquid (Class B) zones typically require much shorter travel distances.
- Assuming coverage is unobstructed — walls, machinery and partitions break up sight lines and walking routes, so more units may be needed in practice.
- Ignoring extinguisher type and rating — the calculator counts units for spacing only, not the correct class or fire rating for the hazards present.
Frequently asked questions
Why is the coverage area 2 × (travel distance)²?
If each extinguisher sits at the centre of a square and the furthest point is a corner, the travel distance is the half-diagonal of that square. For a square of side s the half-diagonal is s/√2, so s = travel × √2 and the area s² = 2 × travel². This is a geometric idealisation, not a code rule.
Does this tell me which extinguishers to install?
No. It only estimates how many units satisfy the travel-distance spacing. The correct type, size and fire rating, plus mounting height, signage and location, must follow the applicable fire code (such as AS 2444) and a competent fire-safety assessment of the actual hazards.
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Tip: Enter any known values to calculate the remaining results.
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