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mg to units calculator
How many units is your dose? The answer depends on one number the question usually leaves out – your concentration.
The short answer
There is no fixed number of units in a milligram. A unit is a volume – 0.01 mL on a U-100 insulin syringe – and a milligram is a mass. What connects them is the concentration of your vial.
units = (dose in mg ÷ concentration in mg/mL) × 100
So 1 mg is 10 units at 10 mg/mL, 100 units at 1 mg/mL and half a unit at 200 mg/mL. Same dose, three answers, because the liquid it is dissolved in is three different strengths.
If a number you were given came from somebody else's vial, it does not transfer to yours. Work it out from your own concentration below.
Convert your dose
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Does "2 mg to units" mean your vial or your dose?
Both readings are common. They give completely different answers, so it is worth being explicit about which one you are asking.
- "My dose is 2 mg." That is the calculation above. Divide by the concentration to get a volume, then multiply by 100 for units.
- "My vial contains 2 mg." A vial strength on its own converts to nothing. A 2 mg vial becomes 2 mg/mL with 1 mL of water or 1 mg/mL with 2 mL, so the same vial produces a different unit count for the same dose depending on how you reconstituted it. Choose the water volume first, then convert.
This is the single most frequent misunderstanding in peptide groups. A post saying "10 units" carries no information unless the reconstitution is posted with it.
1 mg to units at every common strength
The headline case, worked once for each concentration you are likely to meet. All figures are for a U-100 syringe.
| Concentration | 1 mg is | Volume |
|---|---|---|
| 1 mg/mL | 100 units | 1.00 mL |
| 2 mg/mL | 50 units | 0.50 mL |
| 2.5 mg/mL | 40 units | 0.40 mL |
| 5 mg/mL | 20 units | 0.20 mL |
| 10 mg/mL | 10 units | 0.10 mL |
| 20 mg/mL | 5 units | 0.05 mL |
| 25 mg/mL | 4 units | 0.04 mL |
| 50 mg/mL | 2 units | 0.02 mL |
| 100 mg/mL | 1 unit | 0.01 mL |
| 200 mg/mL | 0.5 unit | 0.005 mL |
| 250 mg/mL | 0.4 unit | 0.004 mL |
At 200 mg/mL and above, a 1 mg dose is smaller than one syringe marking. Doses that small are measured with a different tool, not estimated between the lines.
Whole-milligram doses to units
Read down to your dose, across to your concentration. Figures are units on a U-100 syringe.
| Dose | 1 mg/mL | 2 mg/mL | 5 mg/mL | 10 mg/mL | 20 mg/mL |
|---|---|---|---|---|---|
| 1 mg | 100 | 50 | 20 | 10 | 5 |
| 2 mg | 200 | 100 | 40 | 20 | 10 |
| 2.5 mg | 250 | 125 | 50 | 25 | 12.5 |
| 5 mg | 500 | 250 | 100 | 50 | 25 |
| 10 mg | 1000 | 500 | 200 | 100 | 50 |
Anything over 100 units does not fit a 1 mL syringe in one draw. Reconstitute with less water, or split the injection.
Microgram doses to units
Peptides are usually dosed in micrograms. The useful intermediate number is micrograms per unit: vial mg × 10, divided by the mL of water you added.
| Dose | 10 mcg/unit | 20 mcg/unit | 25 mcg/unit | 50 mcg/unit | 100 mcg/unit |
|---|---|---|---|---|---|
| 100 mcg | 10 | 5 | 4 | 2 | 1 |
| 200 mcg | 20 | 10 | 8 | 4 | 2 |
| 250 mcg | 25 | 12.5 | 10 | 5 | 2.5 |
| 300 mcg | 30 | 15 | 12 | 6 | 3 |
| 500 mcg | 50 | 25 | 20 | 10 | 5 |
A 10 mg vial gives 100 mcg per unit with 1 mL of water, 50 with 2 mL, 20 with 5 mL. A 5 mg vial gives half of each.
Check the barrel says U-100
Every figure on this page assumes a U-100 syringe: 100 units per mL, so one unit is 0.01 mL. U-40 syringes are still sold for veterinary insulin at 40 units per mL, where one unit is 0.025 mL.
Draw a U-100 number on a U-40 barrel and you take roughly 2.5× the volume you intended. The two look nearly identical. Read the barrel before every new box.
If you realize after injecting that you drew substantially more than you intended, contact a clinician or your local poison control service rather than waiting to see how it goes. Bring the vial and its concentration with you.
Working it out without the calculator
- 1. Concentration. Vial mg ÷ mL of water = mg per mL. Skip this if the strength is printed on the vial.
- 2. Per unit. mg per mL ÷ 100 = mg in one unit. Multiply by 1000 to read it in micrograms.
- 3. Units. Your dose ÷ the per-unit amount = units to draw.
Worked example: a 10 mg vial with 2 mL of water is 5 mg/mL, which is 50 mcg per unit. A 250 mcg dose is 250 ÷ 50 = 5 units.
Write the per-unit figure on the vial in marker the moment you reconstitute. Almost every dosing error in this space happens weeks later, when somebody is tired and rebuilding the arithmetic from memory.
Frequently asked questions
How many units is 1 mg on an insulin syringe?
It depends on the concentration. At 10 mg/mL, 1 mg is 10 units. At 1 mg/mL it is 100 units, a full 1 mL syringe. At 200 mg/mL, the strength of many testosterone vials, 1 mg is half a unit. The conversion is units = (mg ÷ mg per mL) × 100 on a U-100 syringe.
How many units is 2 mg on an insulin syringe?
At 10 mg/mL, 2 mg is 20 units. At 5 mg/mL it is 40 units, at 20 mg/mL it is 10 units. If the 2 mg refers to the vial rather than the dose, there is no answer yet: the vial strength only becomes a concentration once you decide how much bacteriostatic water to add.
How many units is 200 mcg on a syringe?
Convert the concentration to micrograms per unit first. A 10 mg vial with 2 mL of water is 50 mcg per unit, so 200 mcg is 4 units. The same vial with 5 mL of water is 20 mcg per unit, so 200 mcg is 10 units. Both are correct for the vial they describe.
How many units is 500 mcg?
At 25 mcg per unit, 500 mcg is 20 units. At 50 mcg per unit it is 10 units, at 100 mcg per unit it is 5 units. A 5 mg vial reconstituted with 2 mL of bacteriostatic water gives 25 mcg per unit, which is the most common of those three.
Does the syringe size change the conversion?
No. A 0.3 mL, 0.5 mL and 1 mL U-100 syringe all use the same unit spacing, so a given dose is the same number of units in all three. They differ only in how many units fit: 30, 50 and 100. Pick the smallest barrel that holds your dose, because the markings are further apart and easier to read.
What changes on a U-40 syringe?
A U-40 syringe holds 40 units per mL, so one unit is 0.025 mL rather than 0.01 mL. The formula becomes units = (mg ÷ mg per mL) × 40. A dose that is 10 units on U-100 is 4 units on U-40. Using the wrong one over-doses by 2.5 times, so confirm the barrel is printed U-100.
Sources & further reading
- FDA-approved labeling for Humulin R (regular insulin human injection): "Markings on the U-100 syringe refer to units of less concentrated insulin products ... and NOT units of HUMULIN R U-500", the clearest official statement that syringe markings belong to one concentration
- ISMP, Nurse Advise-ERR, August 2017 – "Problems associated with the use of U-500 insulin syringes": measuring one concentration on another concentration's barrel gives a five-fold error
- DailyMed – Bacteriostatic Water for Injection labeling
- OptiPin tools: full syringe units chart · units to mg · units to mL · reconstitution calculator
The arithmetic here is exact and follows from the definition of U-100. What it cannot verify is what is actually in your vial. Underfilled or mislabeled vials are common enough in this space that the calculation is the floor of your diligence rather than the ceiling.
Not medical advice. This is a unit-conversion reference, not a dosing recommendation. It does not tell you what dose to take, whether a compound is appropriate for you, or whether it is legal where you live. Doses should be set with a prescriber. Nothing here should be used to start, change or stop a medication.
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Enter the vial and the water once. Every future dose shows the units to draw on the dose card, on your phone, with no account and nothing in the cloud.
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