mg to mL Calculator
Volume to give
– mL
Enter the dose and the strength on the label.
- Strength works out to
- –
- Dose
- –
The working
This works out the arithmetic. The order, the product in your hand and local policy still govern what is given.
How many mg are in a mL?
There is no single answer, and that is the whole difficulty. A milligram measures how much medicine there is. A millilitre measures how much liquid there is. Nothing about the two units connects them, so a bare conversion factor between them cannot exist.
What connects them is the strength of the particular product, which is printed on the label. A paracetamol suspension at 250 mg in 5 mL holds 50 mg in every millilitre. The same drug at 125 mg in 5 mL holds half that. Ask for a 500 mg dose and the first gives 10 mL while the second gives 20 mL, twice the liquid for the identical dose.
This is why a conversion chart that claims 1 mL is 1000 mg is describing water rather than medicine. Water happens to weigh a gram per millilitre. A suspension is mostly water too, so it weighs about the same, but almost none of that weight is drug.
How to convert mg to mL
Three numbers, one division:
volume in mL = dose in mg ÷ strength in mg per mL
Where the label gives an amount in a stated volume rather than a per-millilitre figure, work the strength out first. 250 mg in 5 mL is 250 ÷ 5, which is 50 mg/mL. Then divide the dose by it: 500 ÷ 50 is 10 mL.
A dose written in grams or micrograms has to join the same unit ladder before it divides, which is what themcg to mg converter does on its own page. One gram is 1000 mg; one milligram is 1000 mcg.
mg to mL conversion chart for common strengths
Every figure below is the same division run at a different strength. The column that matters most is the middle one: it is the only number that changes the answer.
| Strength on the label | mg in 1 mL | 100 mg dose | 250 mg dose | 500 mg dose |
|---|---|---|---|---|
| Paracetamol 120 mg/5 mL | 24 mg | 4.17 mL | 10.42 mL | 20.83 mL |
| Paracetamol 250 mg/5 mL | 50 mg | 2 mL | 5 mL | 10 mL |
| Acetaminophen 160 mg/5 mL | 32 mg | 3.13 mL | 7.81 mL | 15.63 mL |
| Ibuprofen 100 mg/5 mL | 20 mg | 5 mL | 12.5 mL | 25 mL |
| Ibuprofen 50 mg/1.25 mL | 40 mg | 2.5 mL | 6.25 mL | 12.5 mL |
| Amoxicillin 125 mg/5 mL | 25 mg | 4 mL | 10 mL | 20 mL |
| Amoxicillin 250 mg/5 mL | 50 mg | 2 mL | 5 mL | 10 mL |
| Amoxicillin 400 mg/5 mL | 80 mg | 1.25 mL | 3.13 mL | 6.25 mL |
| Azithromycin 200 mg/5 mL | 40 mg | 2.5 mL | 6.25 mL | 12.5 mL |
| Cefalexin 250 mg/5 mL | 50 mg | 2 mL | 5 mL | 10 mL |
| Prednisolone 15 mg/5 mL | 3 mg | 33.33 mL | 83.33 mL | 166.67 mL |
| Ondansetron 4 mg/5 mL | 0.8 mg | 125 mL | 312.5 mL | 625 mL |
Strengths vary between countries and change between formulations, so the table is a worked illustration and not a product list.
Percent and ratio strengths
Two older notations still appear on ampoules, and both trip people up because neither looks like a strength.
A percentage is grams in 100 mL. Lidocaine 1% is 1 g in 100 mL, so 1000 mg in 100 mL, so 10 mg/mL. Multiplying the percentage by ten gives the mg/mL figure directly, which makes 2% equal 20 mg/mL and 0.9% sodium chloride equal 9 mg/mL.
A ratio is 1 gram in that many millilitres. Adrenaline 1:1000 is 1 g in 1000 mL, which is 1 mg/mL. Adrenaline 1:10,000 is 0.1 mg/mL. The two sit next to each other in a resuscitation trolley and differ tenfold, which is exactly the error the syringe drawing above is there to make visible. Thepercent and ratio converter works in both notations on its own.
Converting mL back to mg
The same relationship read the other way. Multiply instead of dividing:
dose in mg = volume in mL × strength in mg per mL
10 mL of a 50 mg/mL liquid is 500 mg. Switch the first control on the calculator to run it in that direction.
One thing worth watching in this direction is the teaspoon. A teaspoonful on a medicine label means 5 mL, but an actual kitchen teaspoon holds 4.93 mL and varies by several millilitres between spoons, which is why an oral syringe is what comes in the box.
Where mg to mL conversions go wrong
Four failures account for most of them, and none is an arithmetic mistake.
Reading the total, not the strength. A bottle labelled "amoxicillin 100 mL, 250 mg/5 mL" contains 5000 mg. Dividing a dose by 100 mL rather than by the per-millilitre strength is the commonest slip there is.
A strength from memory. The same drug at a second strength is the failure the chart above is built to show. Paediatric and adult formulations of the same medicine routinely differ twofold.
Units that do not match. A dose in micrograms against a strength in milligrams is out by a thousand before the division starts.
Units that are not weight at all. Insulin and heparin are measured in international units, which count biological activity rather than mass. There is no conversion between units and milligrams, so those products need a strength in units per mL, which is what the units to mL calculator takes.
Questions about mg and mL
- How many mg are in a mL?
- There is no fixed answer. A milligram is an amount of medicine and a millilitre is an amount of liquid, so how many milligrams sit in a millilitre depends entirely on the strength of the product. A 250 mg in 5 mL suspension holds 50 mg in every millilitre; a 125 mg in 5 mL suspension of the same drug holds 25 mg.
- What is the formula to convert mg to mL?
- Volume in mL equals the dose in mg divided by the strength in mg per mL. If the label gives an amount in a stated volume instead, divide that amount by that volume first to get the strength per millilitre.
- Is 1 mL always 1000 mg?
- No. That figure comes from water, where 1 mL weighs 1 gram, and it describes the weight of the liquid rather than the amount of drug dissolved in it. A medicine is almost entirely water or another vehicle, so the drug content of a millilitre is set by the strength on the label, not by the density of the liquid.
- How do I read a strength written as a percentage?
- A percentage strength is grams of drug in 100 mL. So 1% is 1 g in 100 mL, which is 1000 mg in 100 mL, which is 10 mg/mL. Multiplying the percentage by 10 gives the strength in mg per mL.
- What does a ratio like 1:1000 mean?
- A ratio strength is 1 gram of drug in that many millilitres. 1:1000 is 1 g in 1000 mL, which is 1 mg/mL. 1:10,000 is 1 g in 10,000 mL, which is 0.1 mg/mL, a tenfold difference from the first.