100-hour fuels are standard dead fuels with diameters ranging from 1 to 3 inches (~2–7 cm). Due to their larger size, the moisture content of 100-hour fuels responds more slowly to changing weather conditions. These fuels can also serve as an indicator of the average moisture content of the forest floor. 100-hour fuel moisture is expressed as a percentage, where lower values indicate drier conditions.
In Canada, the closest equivalent is the Duff Moisture Code (DMC).