Method: For a rectangular sharp-crested weir: Q = (2/3) × C_d × b × √(2g) × h^3/2 where b is weir width and h is head above the crest. For a V-notch weir: Q = (8/15) × C_d × tan(θ/2) × √(2g) × h^5/2 where θ is the included notch angle. Dimensions are converted internally to metres before calculation. These equations provide general sharp-crested weir estimates. Accurate flow measurement depends on correct head measurement, free nappe ventilation, approach conditions, contraction, notch geometry and an appropriate discharge coefficient. Standard calibrated weirs may use more specific rating equations or coefficient corrections. Use the applicable standard or calibration data when high measurement accuracy is required.