Drain Size (\( d = 52.2 (Dc \cdot A \cdot n)^{0.375} s^{-0.1875} \)):

Where:

• \( d \) is the inside diameter, in millimeters (mm).
• \( Dc \) is the drainage coefficient, in millimeters per day (mm/day).
• \( A \) is the drainage area, in hectares (ha).
• \( n \) is the roughness coefficient.
• \( s \) is the drain slope, in meters per meter (m/m).