How many units is a mg amount?
Divide the amount in mg by the concentration in mg per mL, then multiply by 100. That gives units on a U-100 syringe. The concentration is what makes the same mg read differently in two vials.
The direct answer
Units equal mg divided by mg per mL, times 100. A U-100 syringe is marked so that 100 units is exactly 1 mL, which is why the multiplier is always 100 and never changes with the barrel size.
units = (mg ÷ mg/mL) × 100
The concentration comes from the vial: vial mg divided by the millilitres of bacteriostatic water added. 10 mg in 2 mL gives 5 mg/mL, so 10 units on a U-100 syringe contains 0.5 mg.
This page is arithmetic only. It converts numbers you already have from the vial in front of you and the prescription you were given. It does not tell you how much water to add, how much to take, or how often. Those are medical decisions for a licensed clinician who knows your history.
Five worked examples
10 ÷ 2 = 5 mg/mL. An amount of 0.5 mg is 0.5 ÷ 5 = 0.1 mL, which reads 10 units on a U-100 syringe.
10 ÷ 2 = 5 mg/mL. An amount of 2 mg is 2 ÷ 5 = 0.4 mL, which reads 40 units on a U-100 syringe.
5 ÷ 2 = 2.5 mg/mL. An amount of 0.5 mg is 0.5 ÷ 2.5 = 0.2 mL, which reads 20 units on a U-100 syringe.
30 ÷ 3 = 10 mg/mL. An amount of 6.75 mg is 6.75 ÷ 10 = 0.675 mL, which reads 67.5 units on a U-100 syringe.
2 ÷ 1 = 2 mg/mL. An amount of 0.5 mg is 0.5 ÷ 2 = 0.25 mL, which reads 25 units on a U-100 syringe.
Reference table: units on a U-100 syringe
Concentration down the side, amount across the top. Blank cells are draws over 100 units, which will not fit in a single 1 mL barrel.
| Concentration | 0.25 mg | 0.5 mg | 1 mg | 2 mg | 2.5 mg | 5 mg |
|---|---|---|---|---|---|---|
| 1 mg/mL | 25 u | 50 u | 100 u | over 100 u | over 100 u | over 100 u |
| 2 mg/mL | 12.5 u | 25 u | 50 u | 100 u | over 100 u | over 100 u |
| 2.5 mg/mL | 10 u | 20 u | 40 u | 80 u | 100 u | over 100 u |
| 5 mg/mL | 5 u | 10 u | 20 u | 40 u | 50 u | 100 u |
| 6 mg/mL | 4.2 u | 8.3 u | 16.7 u | 33.3 u | 41.7 u | 83.3 u |
| 10 mg/mL | 2.5 u | 5 u | 10 u | 20 u | 25 u | 50 u |
What 20 units looks like
Questions people actually type
How much is 0.5 mg on a U-100 syringe?
It depends entirely on the concentration, so 0.5 mg has no single unit reading. At 5 mg/mL, 0.5 mg is 10 units. At 2.5 mg/mL the same 0.5 mg is 20 units, and at 10 mg/mL it is 5 units. Work out mg divided by mg/mL first to get millilitres, then multiply by 100 to get units on a U-100 barrel.
6.75 mg is how many units on a syringe?
At 10 mg/mL, 6.75 mg is 67.5 units. At 5 mg/mL it would be 135 units, which is more than a 1 mL U-100 barrel holds, so it could not be drawn in one go. The concentration has to be known before the question has an answer: divide 6.75 by the mg/mL figure, then multiply by 100.
What is 2 mg on a 100 unit syringe?
At 5 mg/mL, 2 mg is 40 units. At 10 mg/mL it is 20 units, and at 2.5 mg/mL it is 80 units. A 100 unit syringe holds 1 mL, so the unit mark you are reading is a volume mark, not a mass mark. The mass depends on how concentrated the liquid in the barrel is.
What is 7.50 units on a 1 mL syringe?
On a 1 mL U-100 syringe, 7.5 units is 0.075 mL, because 100 units is 1 mL. What that volume weighs depends on concentration: at 5 mg/mL it is 0.375 mg, and at 10 mg/mL it is 0.75 mg. Units measure volume, so a mass answer needs the mg/mL figure as well.
How many milligrams is 40 units if you reconstitute with two mL of bac water?
Two millilitres of water alone does not fix the answer, because the vial mass matters too. 40 units is 0.4 mL on a U-100 syringe. With a 10 mg vial in 2 mL you have 5 mg/mL, so 0.4 mL is 2 mg. With a 5 mg vial in the same 2 mL you have 2.5 mg/mL, so the same 40 units is 1 mg.
Related conversions
Worked vial cases
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