An elutriation system was developed to estimate weed seed densities in soil. The system provided reliable estimates of seed densities for weed species with a broad range of seed weights (0.06 to 9.80 mg) and had no effect on seed viability of three weed species tested. Elutriation of soil samples (up to 60 g) taken from a cultivated field took approximately 15 min. Separating, classifying, and counting seeds is time consuming (20 to 30 min per sample) but provides an accurate estimate of seed densities for weeds with a diameter of 0.5 mm or more.