A large collection of laboratory measurements on piezometric head (h) and discharge (Q) are made over hydraulic models of an inclined rectangular weir at nine different angles, ranging from 25.7 to 90 degrees within a 0.3-m wide flume. These measurements are corroborated with additional laboratory data taken within a 1-m wide flume across four inclination angles. The range of both inclination angle (θ) and flow scale examined in this study elucidate the nature of the head-discharge rating equation beyond previous work. Results show that as θ decreases under a constant Q, the h over the weir decreases in a monotonic fashion due to the shallower angle of attack of the flow, which results in less curvature of the streamlines over the crest and therefore less deviation from the upstream hydrostatic pressure condition. To incorporate this effect into the head-discharge rating equation, a transformation of the h term is applied by multiplying the measured h that occurs over an inclined weir by a correction factor to match the effective h that would occur if the weir were aligned perpendicular to the flow at the same discharge. Thus, a modified form of the classical sharp-crested weir rating equation can be used as a means for determining the value of Q for inclined cases to a high degree of accuracy. The degree of accuracy depends upon dimensionless Reynolds and Weber numbers describing the flow inertia in the approach to the weir in relation to respective viscous and surface tension scale effects. This approach portends marked flow measurement enhancement for flow conditions above a suggested inertial threshold.