Convert milligrams (mg) to milliliters (mL) — or mL back to mg — using the substance's density or a medication's concentration. Because mg measures weight and mL measures volume, the conversion depends on how much the liquid weighs per mL. Pick a substance to fill the density automatically, or enter your own. Leave the value you want to find blank.
The mg to mL calculator converts a weight in milligrams into a volume in milliliters — and works in reverse, too. This is one of the most common conversions in medicine, cooking, chemistry, and the laboratory, yet it trips many people up, because milligrams and milliliters measure completely different things. A milligram is a unit of mass (weight), while a milliliter is a unit of volume (space). To convert between them you need one extra piece of information: the substance's density, or, for a medicine, its concentration. This calculator has the densities of common liquids and the concentrations of popular medications built in, so you can convert accurately in a single click.
Whether you are working out a liquid medication dose, converting a recipe, or preparing a solution in the lab, this tool bridges the gap between weight and volume quickly and reliably. Below you will find a clear explanation of the formula, worked examples you can reproduce, the built-in presets, and answers to the questions people ask most often.
Milligrams and milliliters are not interchangeable, because they measure different physical properties. Weight (mass) tells you how much matter something contains; volume tells you how much space it occupies. The link between the two is density — how much mass is packed into each unit of volume. Water, for example, has a density of about 1 gram per milliliter (1000 mg/mL), so 1000 mg of water occupies exactly 1 mL. But oil is lighter (about 916 mg/mL), so the same 1000 mg of oil takes up a little more space, and honey is much denser, so it takes up less.
This is why there is no single "mg to mL" number that works for everything. The conversion always depends on what substance you are measuring. For medications, the relevant figure is the concentration — how many milligrams of the active drug are dissolved in each milliliter of liquid — which plays the same mathematical role as density in the formula.
The conversion uses one simple equation:
volume (mL) = weight (mg) ÷ density (mg/mL)
and, rearranged to go the other way:
weight (mg) = volume (mL) × density (mg/mL)
In words: to turn milligrams into milliliters, divide the weight by the density; to turn milliliters into milligrams, multiply the volume by the density. When you are working with water, whose density is 1000 mg/mL, the formula simplifies to mL = mg ÷ 1000, which is where the familiar rule "1000 mg of water = 1 mL" comes from.
Suppose you have 5 grams of water, which is 5,000 mg. Dividing by the density of water (1000 mg/mL):
5,000 mg ÷ 1000 mg/mL = 5 mL
So 5,000 mg of water is exactly 5 mL. These are the default values in the calculator, so you can press Calculate to see the result, then change the substance or the numbers.
Say a liquid medicine has a concentration of 20 mg/mL and you need a 50 mg dose. The volume to measure is:
50 mg ÷ 20 mg/mL = 2.5 mL
So you would draw up 2.5 mL of that medicine. This is exactly how nurses and pharmacists convert a prescribed dose in milligrams into a volume they can measure with a syringe.
Going the other way, suppose you have 25 mL of cooking oil and want its weight. With oil's density of 916 mg/mL:
25 mL × 916 mg/mL = 22,900 mg
So 25 mL of cooking oil weighs 22,900 mg, or about 22.9 grams.
The calculator includes presets so you do not have to look up densities yourself. Selecting a substance fills in its density (or a medication's concentration) automatically, and you can always override it with your own value.
For anything not on the list, choose Custom and type the density or concentration directly.
Nowhere is the mg-to-mL conversion more important than in dosing liquid medicines. Prescriptions and dosing guidelines are usually given in milligrams of the active ingredient, but liquid medicines are measured out in milliliters. Converting between the two correctly is essential for safe dosing, especially for children, where doses are small and errors can be serious.
The key number is the medication's concentration, printed on the label as something like "100 mg/5 mL" or "10 mg/mL." That tells you how many milligrams of the drug are in each milliliter of liquid. To find the volume for a given dose, divide the dose in milligrams by the concentration. For instance, if a child needs 150 mg of an ibuprofen suspension labeled 100 mg/5 mL (which is 20 mg/mL), the volume is 150 ÷ 20 = 7.5 mL. Always double-check the concentration on your specific product, since the same drug is sold in different strengths, and follow the dosing instructions from a doctor or pharmacist.
Recipes sometimes list ingredients by weight and sometimes by volume, and converting between the two is handy when you only have one type of measuring tool. For water-based liquids, the conversion is nearly one-to-one in grams and milliliters, but for oils, syrups, and other ingredients the density matters. Cooking oil, at about 916 mg/mL, is lighter than water, so a given weight of oil takes up slightly more volume. Honey and syrups, being denser than water, take up less. Using the correct density — or a dedicated ingredient converter for solids like flour and sugar — keeps your measurements accurate.
In chemistry and biology, converting between mass and volume is routine when preparing solutions and reagents. A solution's concentration, often given in mg/mL or as a percentage, lets you calculate how much liquid contains a required mass of solute, or how much solute is present in a given volume. The same simple formula — volume equals mass divided by density or concentration — underlies these calculations. Being comfortable moving between milligrams and milliliters is a basic laboratory skill, and this calculator makes it quick while you keep your attention on the experiment.
It is worth being clear about the two quantities that drive this conversion, because they are closely related but not identical.
In the mg-to-mL formula, both play the same role — the "mg per mL" figure you divide or multiply by. For a pure liquid, use its density; for a medicine or a made-up solution, use its concentration. Just make sure the value is expressed in mg/mL, converting first if your figure is given per 5 mL, per liter, or as a percentage.
Here are some frequently needed conversions for water (density 1000 mg/mL), where the numbers are especially clean:
For substances other than water, these figures change in proportion to the density. For a medicine at 20 mg/mL, for example, 100 mg is 5 mL, and 500 mg is 25 mL — because each milliliter carries only 20 mg instead of 1000.
Both the milligram and the milliliter belong to the metric system, which is built on tidy powers of ten — and that makes the surrounding conversions easy once you separate weight from volume. On the weight side, 1 gram is 1,000 milligrams, and 1 kilogram is 1,000 grams (a million milligrams). On the volume side, 1 liter is 1,000 milliliters, and a milliliter is exactly the same as a cubic centimeter (cc), a unit you often see on syringes. The reason a milliliter of water conveniently weighs about one gram is a deliberate feature of the metric system: it was originally defined so that one liter of water would weigh one kilogram. That neat coincidence holds only for water and substances of similar density, which is why every other conversion needs the density step. Keeping the two ladders — the weight ladder (mg, g, kg) and the volume ladder (mL, L) — clearly in mind, with density as the bridge between them, removes almost all the confusion people feel about this conversion.
It can feel counter-intuitive that 1,000 mg turns into 1 mL of water but a different volume of oil or syrup. The reason is entirely about how tightly packed each substance is. Denser substances squeeze more mass into each milliliter, so a fixed weight occupies less volume; lighter substances spread the same mass over more space. Honey, for example, is roughly 1.4 times as dense as water, so 1,000 mg of honey is only about 0.7 mL, while 1,000 mg of cooking oil (lighter than water) is about 1.09 mL. For medications the "density" is really the concentration, which is chosen by the manufacturer and can differ enormously between a dilute pediatric syrup and a concentrated injection of the very same drug. This is exactly why you should never assume a conversion from one product to another — always read the concentration on the label of the specific bottle in your hand, and let the calculator do the arithmetic with that number.
Divide the weight in milligrams by the density (or concentration) in mg/mL: mL = mg ÷ density. For water, density is 1000 mg/mL, so you simply divide the milligrams by 1000.
Only for water and substances with the same density. Because water is 1000 mg/mL, 1000 mg of water is 1 mL. For other substances you must use their own density or concentration.
Divide the dose in milligrams by the medicine's concentration in mg/mL. For example, a 50 mg dose of a 20 mg/mL solution is 50 ÷ 20 = 2.5 mL. Always confirm the concentration on your product's label.
Because milligrams measure weight and milliliters measure volume, and density is what links them. Without it there is no way to know how much space a given weight occupies, since different substances have different densities.
Yes. Enter a weight in mg to get the volume in mL, or enter a volume in mL to get the weight in mg. Just leave the value you want to find blank.
Divide the milligrams by the milliliters: 100 ÷ 5 = 20 mg/mL. The medication presets in this calculator already convert these labels into mg/mL for you.
This mg to mL Calculator is provided for general informational and educational purposes. Densities and medication concentrations are approximate and can vary by product, temperature, and formulation. It is not medical advice; always follow the dosing instructions of a qualified healthcare professional and the product label when measuring medication.