WILDFIRE ENGINEERING TOOL · BYRAM RELATIONSHIP
Flame Length Calculator
Translate fireline intensity into estimated flame length—or work backwards from an observed flame length. See the equation, unit conversions and operational context in one reproducible view.
Range: 0–10,000 kW/m. You may type a larger value.
Relationship used
L = 0.0775 × I0.46L in metres · I in kW/mCALCULATED ESTIMATE
4.44 ft flame length
Historical suppression interpretation
Lower flame-length class
Within the lowest flame-length band used in historical fire-behaviour guidance.
READ THE RESULT CORRECTLY
An empirical relationship, not a fire forecast.
This calculator applies the Byram relationship to a single value. It does not model wind, slope, fuel arrangement, flame tilt, spotting, crown fire or changing conditions.
Do not use the result as a safety distance, evacuation threshold or substitute for local incident information. Observed flame length and calculated flame length are not interchangeable in every fire environment.
Interpretation bands
Lowest historical band.
Direct attack becomes more difficult.
Serious control problems may occur.
High-intensity behaviour; direct head attack historically described as ineffective.
Method and sources
Forward: L = 0.0775 I0.46. Inverse: I = (L / 0.0775)1/0.46. Conversion: 1 Btu/(ft·s) = 3.46147 kW/m; 1 m = 3.28084 ft.
The relationship is a compact empirical estimate. Recent experimental work shows flame-zone geometry can affect the intensity–length relationship, so treat the output as context, not ground truth.
USDA Forest Service: SI reformulation · NWCG interpretation guidance