How this calculator works
Milligrams measure mass and millilitres measure volume, so a conversion needs a link between them. For a pure liquid that link is its density, expressed in milligrams per millilitre. Water is close to 1,000 mg/mL, so 1,000 mg of water is 1 mL. For a liquid medicine the same number is the concentration printed on the label: a bottle of 100 mg per 5 mL contains 20 mg in each millilitre. Enter that concentration in the custom row and the page gives the volume that contains the mass you entered. The page does not decide whether the resulting volume or dose is appropriate.
Formula
milligrams = value x 1,000 if the mass is in grams, or / 1,000 if it is in micrograms. millilitres = milligrams / density in mg/mL. For a labelled concentration, mg/mL = strength in mg / volume in mL, so 100 mg in 5 mL is 20 mg/mL. Litres = millilitres / 1,000, US teaspoons = millilitres / 4.92892159375 and US tablespoons = millilitres / 14.78676478125.
Worked example
1,000 mg of water 1,000 mg/mL gives 1 mL, which is 0.202884 tsp and 0.0338140 fl oz. 2.5 g of milk at 1,030 mg/mL gives 2.42718 mL. 1,000 mg of cooking oil at 920 mg/mL gives 1.08696 mL. A medicine at 100 mg per 5 mL has a concentration of 20 mg/mL, so 50 mg of it is 2.5 mL.
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Frequently asked questions
Why is there no single mg to mL answer?
Because mass and volume are different quantities. One milligram of water and one milligram of oil occupy different volumes. You need the density of the liquid, or for a medicine the concentration on its label.
How do I enter a medicine concentration?
Divide the strength by the volume. For 100 mg per 5 mL, enter 100 / 5 = 20 mg/mL. For 400 mg per 5 mL, enter 80 mg/mL. Then enter the mass you need and read the volume.
Are the spoon measures accurate enough for medicine?
No. Household teaspoons vary in volume by a large margin. Use a marked oral syringe or the measuring device supplied with the medicine. The spoon rows here are ordinary US customary conversions, not dosing instructions.
Is the density of milk always 1,030 mg/mL?
No. Milk density varies with fat content and temperature, and the value here is a typical whole milk figure. Use the custom row for a value from a specific product or reference.