WILDFIRE FIELD MATH · LINEAR SPREAD
Wildfire Rate of Spread Calculator
Solve the relationship between spread rate, distance and elapsed time. Convert the result instantly across metric, US customary and wildland-fire units.
Context labels the result only; it does not change the arithmetic.
R = D ÷ TAll inputs are converted internally to metres and minutes before calculation.CALCULATED RESULT
Forward/head spread
300 m ÷ 30 min = 10 m/min
CONSTANT-RATE EQUIVALENTS
Same rate, different time windows.
These distances are simple linear extrapolations of the calculated rate. They are not a wildfire forecast.
INTERPRET WITH CARE
A measured relationship—not a behaviour model.
This tool solves rate = distance ÷ time. It does not estimate how fuels, wind, slope, moisture, suppression actions or spotting will change a fire.
Identify whether an observation represents head, flank or backing spread. Do not combine linear rate, perimeter growth and area growth as though they were the same quantity.
Never use this calculator as an evacuation clock, safety-zone calculation or substitute for official incident information.
Units and definitions
What this calculator means by rate of spread
Here, rate of spread means the speed at which a selected point or segment of a fire front moves horizontally across the landscape. NWCG notes that the broader term can also describe perimeter or area increase, so the measurement type must always be stated.
NWCG: Forward rate of spread · NWCG: Rate of spread field math · USDA Forest Service: units and conversions
Quick answers
Does this predict future wildfire spread?
No. It calculates one missing value from two supplied values under a constant-rate assumption.
Why include chains per hour?
Chains per hour remains a common linear spread-rate unit in US wildland-fire practice. One chain equals 66 feet.
Can I calculate flank or backing spread?
Yes, if the distance and elapsed time correspond to that specific part of the fire. Select the context so the result remains unambiguous.