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Vegetation in a constructed stormwater wetland (CSW) is essential for nutrient removal and thermal pollution reduction. However, a portion of the storage volume designed to retain the water quality event is occupied by vegetation, which may result in the CSW being under-sized from a hydrologic perspective. Twelve stormwater wetlands and one hybrid wet pond in North Carolina were sampled to document their percent vegetative occupancy by volume. Vegetation was harvested from randomly selected 0.1 m2 areas at the normal pool elevation, and displacement tests were used to calculate the volume added by vegetation at elevations of 30 cm and 45 cm. Combining these data with observed vegetative cover, a water quality volume factor of safety accounting for vegetative occupancy was calculated for use in CSW design.