1g of oil is 12.5ml ..

g is the unit of weight, and ml is the unit of volume. If you want to convert, you need to know the density of the material, and the mass is equal to the product of volume and density. The density of water is exactly 1, so a millilitre of water is exactly one gram. For water, milliliters are exactly equal to grams. For oil, the density of oil is .8. One milliliter of oil multiplied by .8 equals .8 grams. One gram of oil divided by .8 equals 12.5 ml.