Fine Fuel Moisture (FFM) is the moisture content of a specific fuel size expressed as percent.

• A. The moisture content of all fuels
• B. The moisture content of a specific fuel size expressed as percent
• C. The weight of fuels
• D. The temperature of fuels

Answer: (B)

Fine Fuel Moisture measures how much water is in the smallest fuels, but it does so for a defined fuel size and expresses that amount as a percentage of the dry weight. Those fine fuels—like grasses and small twigs—dry and wet quickly, so using a specific size class lets you compare conditions consistently across sites and times. The moisture value is calculated as the percentage of water in the fuel relative to its dry weight, typically (wet weight − dry weight) ÷ dry weight × 100. This focus on a particular fuel size and a percent value distinguishes FFM from overall fuel weight or fuel temperature, and it provides a practical measure for predicting ignition and spread in prescribed fire planning.