Rate of spread is the amount of time it takes for the leading edge of a fire to travel from point A to point B, and is commonly measured in miles per hour or feet per minute. Factors that affect rate of spread include weather (e.g., wind speed, relative humidity, temperature), fuel (e.g., moisture, arrangement, size, load, type), and topography (e.g., slope, aspect, elevation, configuration). Calculating (potential) rates of spread is useful when planning and preparing for prescribed fires as well as when suppressing spot fires and wildfires.