We offer 4 sizes, 250mg, 500mg, 750mg, and 1000mg. The bottles are all the same size, 1oz (30ml). The mg refers to the amount of Oil added to the bottle. The 250 is often used for pets as it is the weakest formula. Most people use the 500, 750 and 1000 mg bottles. They provide 16, 24 and 33 mg of cbd per serving, with 30 servings per bottle. Some people take one serving a day while others take 100-200mg a day. The more concentrated the bottle the better price you get per mg of CBD.