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Fire Load Density Calculator

Work out fire load density instantly with clear inputs, formula shown and shareable results.

About Fire Load Density Calculator

Fire load density is the total heat that could be released by the combustible contents divided by the floor area, in megajoules per square metre. It is often quoted as an equivalent mass of wood, at 18 MJ/kg, and it drives required fire resistance periods and sprinkler hazard classification.

Formulas

Fire load density

MJ/m² = combustible mass x calorific value / floor area

Wood equivalent

kg/m² = MJ/m² / 18

Worked example

With the default values below, Fire Load Density Calculator returns Fire load density of 360.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Mass of combustible contentsminimum 0.1 kg
5,000 kg
Average calorific valueminimum 0.1 MJ/kg
18 MJ/kg
Floor areaminimum 0.1 m²
250 m²

Results

Fire load density
360.0 MJ/m²
Total fire load
90,000 MJ
Wood equivalent
20.0 kg/m²
Indicative hazard class
Low fire load — light hazard

Step by step

  1. 1Values used
  2. 2Fire load density
  3. 3Wood equivalent
  4. 4Fire load density= 360.0 MJ/m²
  5. 5Total fire load= 90,000 MJ
  6. 6Wood equivalent= 20.0 kg/m²
  7. 7Indicative hazard class= Low fire load — light hazard

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Fire load assessment and the resulting fire resistance requirements must be determined by a qualified fire engineer to the applicable code.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Fire load assessment and the resulting fire resistance requirements must be determined by a qualified fire engineer to the applicable code.

Frequently Asked Questions

How is the Fire Load Density figure worked out?

MJ/m² = combustible mass x calorific value / floor area. Fire load density is the total heat that could be released by the combustible contents divided by the floor area, in megajoules per square metre.

Should the building structure be included?

Fixed combustible construction such as timber framing and linings is added to the movable contents where it can contribute to the fire. Non-combustible structure is excluded.

What values do I need to enter?

This calculator takes 3 inputs: Mass of combustible contents, Average calorific value, Floor area. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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