Question: how many grains of sand in 1 kg?
Answer: so 1 kg ≈ 0.69 L. One common estimate for the average diameter of a sand grain is 0.8 mm. Treating the grain as a sphere, for simplicity, its volume is about 0.268 µL. (0.69 L)/(0.268 µL/grain) = 2.57 million grains (approximately).