Move the sliders and watch Byram’s fireline intensity update instantly from heat content, flaming fuel consumption and rate of spread.
Drag any slider. The value and calculation update immediately.
How to calculate fireline intensity: a worked unit conversion
The calculator uses I = H × w × r. Enter heat of combustion in MJ/kg, flaming fuel consumption in kg/m² and spread rate in m/s. The result is in kW/m; the calculation converts MJ to kJ.
Example with spread measured in metres per minute: assume H = 18 MJ/kg, w = 1 kg/m² and spread = 6 m/min. First divide 6 by 60 to obtain 0.1 m/s. Then calculate 18,000 × 1 × 0.1 = 1,800 kW/m.
This is an illustrative calculation using chosen inputs, not a measured incident. Entering 6 as m/s instead of converting 6 m/min would make this result 60 times too large.
Try these inputs in the calculator ↑ · Convert wildfire units
Check each input before comparing results
- Keep the heat value’s MJ/kg input separate from the kJ/kg value used in the equation.
- Use the flaming fuel consumption required by this model, rather than substituting a different fuel quantity without explanation.
- Record the spread-rate unit alongside the number.
Continue with the fireline intensity definition, rate-of-spread calculator or flame-length calculator and its assumptions.
Move any slider above and the result changes immediately. Byram’s relationship is directly proportional to all three variables, so increasing one input while holding the others constant increases calculated fireline intensity by the same proportion.
With a low heat of combustion of 18 MJ/kg, flaming fuel consumption of 1 kg/m² and rate of spread of 0.02 m/s:
18,000 × 1 × 0.02 = 360 kW/m