The Chandler Burning Index (CBI) uses the air temperature and relative humidity to calculate a numerical index of fire danger. That number is then equated to the Fire Danger severity of either extreme, very high, high, moderate, or low. It's based solely on weather conditions, with no adjustment for fuel moisture.

The Fire Weather Index (FWI) is based on weather readings taken at noon standard time and rates fire danger at the mid afternoon peak from 2:00 – 4:00 pm.

To interpret the system, the three fuel moisture codes and the three behaviour indices need to be understood. Each code and index is a numerical rating related to likely fire behaviour. The scales start at zero, and except for the Fine Fuel Moisture Code which has a maximum of 99, all are open-ended. Low ratings indicate high moisture content, and ratings rise as moisture content decreases. Ratings rise as fire weather becomes more severe.

Weather readings required are:

The Fire Weather Index has six components:

Three Fuel Moisture Codes:

Three Fire Behaviour Indices:

The DC is a numerical rating of the moisture content of deep, compact, organic layers. It is a useful indicator of seasonal drought and shows the likelihood of fire involving the deep duff layers and large logs. A long period of dry weather (the system uses 52 days) is needed to dry out these fuels and affect the Drought Code. A DC rating of 200 is high, and 300 or more is extreme indicating that fire will involve deep sub-surface and heavy fuels. Burning off should not be permitted when the DC rating is above 300.

The Build Up Index (BUI) shows the amount of fuel available for combustion, indicating how the fire will develop after initial spread. It is calculated from the Duff Moisture Code and the Drought Code.

The BUI scale starts at zero and is open-ended. A rating above 34 is high, above 77 is extreme.

The Initial Spread Index (ISI) indicates the rate fire will spread in its early stages. It is calculated from the FFMC rating and the wind factor.

The open-ended ISI scale starts at zero and a rating of 10 indicates high rate of spread shortly after ignition. A rating of 19 or more indicates extremely rapid rate of spread.

The Fine Fuel Moisture Code (FFMC) is a numerical rating of the moisture content of surface litter and other cured fine fuels. It shows the relative ease of ignition and flammability of fine fuels. The moisture content of fine fuels is very sensitive to the weather. Even a day of rain, or of fine and windy weather, will significantly affect the FFMC rating. The system uses a time lag of two-thirds of a day to accurately measure the moisture content in fine fuels. The FFMC rating is on a scale of 0 to 99. Any figure above 70 is high, and above 90 is extreme.

The Drought Factor (DF) is a key component of the FFDI is the modelling of the dryness of the fuel. This is expressed by the Drought Factor (DF), which ranges from 0 to 10. If this is multiplied by 10 and called a percent, it gives the percentage of fine fuel that would be removed by a fire under the current conditions.

The DF is based on recent rainfall and on the Byram-Keetch Drought Index (BKDI).

The Grass Fire Danger Code (GFD) is based on predicted generated "fire intensity (kw/m²)" in grass type vegetation (dry grass, tussock). This code denotes how difficult it would be to control a fire in this vegetation type should one start.

The Scrub Fire Danger Code (SFDC) is based on predicted generated "fire intensity (kw/m²)" in flammable scrub type vegetation (tea tree, broom, gorse, manuka). This code denotes how difficult it would be to control a fire in this vegetation type should one start.

The Forest Fire Danger Code (GFFDC) is based on predicted generated "fire intensity (kw/m²)" in grass type vegetation (dry grass, tussock). This code denotes how difficult it would be to control a fire in this vegetation type should one start.