The formula to calculate the flame height in a biomass cookstove is:

\[ FH = C \cdot P^{2/5} \]

Where:

• \(FH\) is the flame height in millimeters (mm).
• \(C\) is the grate constant, 76 mm/KW for fire with grate, and 110 mm/KW for fire without grate.
• \(P\) is the power output in KCal/hr.