mg to mL Calculator
Milligrams (mg) measure mass and milliliters (mL) measure volume, so you need one more piece of information to convert between them: either the density of a liquid or the concentration of a medication. Choose your mode, pick a preset substance or enter your own value, and this calculator works out the volume from the mass or the mass from the volume, with the full working shown below the result.
Why you cannot convert mg to mL without more information
Milligrams (mg) measure mass, the amount of matter in a substance. Milliliters (mL) measure volume, the space a substance occupies. You cannot switch between the two without knowing how densely packed the substance is. For pure water at room temperature, 1 mL weighs exactly 1 gram (1000 mg), so 500 mg of water is 0.5 mL. But 500 mg of honey occupies only about 0.352 mL because honey is much denser. For medications, the relevant value is concentration rather than raw density: a 10 mg/mL solution means every milliliter contains 10 mg of active ingredient, so a 50 mg dose requires 5 mL.
The two conversion formulas
When converting from mass to volume: mL = mg / (mg per mL). When converting from volume to mass: mg = mL x (mg per mL). The "mg per mL" value is either the density of the liquid (for pure substances like water or oil) or the concentration stated on a medication label (for drug solutions). If a label says "250 mg per 5 mL", divide 250 by 5 to get 50 mg/mL before using the formula.
Medication dosing: reading the label correctly
Liquid medications express strength in two main ways. The first is mg/mL, for example "ibuprofen 20 mg/mL" means each milliliter contains 20 mg. The second is mg per fixed volume, for example "amoxicillin 400 mg/5 mL" means every 5 mL contains 400 mg, which works out to 80 mg/mL. Always divide the milligram amount by the volume amount to get mg/mL, then apply the formula. Check the label every time because the same drug name can come in several different concentrations, and using the wrong one leads to under- or over-dosing. This calculator provides preset concentrations for common medications as a convenience, but you should always verify against the actual label in front of you.
Precision and measurement tools
Volumes below about 0.5 mL are difficult to measure accurately with a standard kitchen spoon or even a typical oral syringe. For small volumes, use a calibrated oral syringe (available at pharmacies) or, in a laboratory context, a micropipette. Most oral syringes mark every 0.1 mL or 0.2 mL, which is sufficient for most pediatric doses but can introduce errors of a few percent at very small volumes. For cooking and baking, a kitchen scale is often more accurate than volume measurement for dense ingredients like honey or oil.
Density of common liquids (mg/mL)
| Substance | Density (mg/mL) | mg per 1 mL | mL per 1000 mg |
|---|---|---|---|
| Water | 1000 | 1000 | 1.000 |
| Whole milk | 1030 | 1030 | 0.971 |
| Blood (whole) | 1060 | 1060 | 0.943 |
| Cooking oil (vegetable) | 916 | 916 | 1.092 |
| Honey | 1420 | 1420 | 0.704 |
| Ethanol (ethyl alcohol) | 789 | 789 | 1.267 |
| Glycerin (glycerol) | 1261 | 1261 | 0.793 |
These approximate values apply at room temperature (~20 degrees C / 68 degrees F). Use them to convert a mass in mg to a volume in mL.
Frequently asked questions
Is 1 mg equal to 1 mL?
Only for water at room temperature, because water has a density of 1 g/mL (= 1000 mg/mL), so 1 mg of water occupies 0.001 mL, not 1 mL. People sometimes confuse this because 1 gram of water = 1 mL, but 1 milligram is one-thousandth of a gram, so 1 mg of water = 0.001 mL. For any substance other than water, the ratio is different because the density differs.
How do I convert mg/5 mL to mg/mL?
Divide the milligram amount by the milliliter amount. For "250 mg/5 mL", divide 250 by 5 to get 50 mg/mL. For "400 mg/5 mL", divide 400 by 5 to get 80 mg/mL. This calculator does that conversion automatically when you enter a medication preset.
How many mL is 500 mg?
It depends on the substance. For water (density 1000 mg/mL), 500 mg = 0.5 mL. For a medication labeled 50 mg/mL, 500 mg = 10 mL. For cooking oil (density approximately 916 mg/mL), 500 mg is about 0.546 mL. Without knowing the density or concentration, the question cannot be answered.
Can I use this to calculate a medication dose for my child?
This calculator can help you find the volume that corresponds to a prescribed dose, but it does not determine what dose is appropriate. Always have the dose confirmed by a doctor or pharmacist before giving any medication. Double-check the concentration on the actual label in front of you because the same drug name comes in different strengths.
What is the density of water in mg/mL?
Pure water at 20 degrees C has a density of approximately 1.000 g/mL, which is 1000 mg/mL. This is the standard reference density. Saltwater, milk, and other water-based liquids are slightly denser because dissolved or suspended material adds mass without proportionally increasing volume.
How do I convert mL back to mg?
Multiply the volume in mL by the density or concentration in mg/mL. For example, 2.5 mL of a 20 mg/mL solution contains 2.5 x 20 = 50 mg. Switch the calculator direction to "Mass from volume" to have it done automatically.