What is the formula of blast furnace gas calorific value?

The formula to calculate the calorific value of blast furnace gas is: Calorific value (MJ/m³) = 0.313 x %CO + 0.313 x %H2 + 0.093 x %CH4. In this formula, %CO represents the percentage of carbon monoxide, %H2 represents the percentage of hydrogen, and %CH4 represents the percentage of methane in the blast furnace gas.