Question 1

How do you convert mg to units?

Accepted Answer

Divide the milligrams of peptide in your vial by the millilitres of water you added — that is your concentration in mg/mL. Then divide your dose in milligrams by that concentration to get the volume in millilitres, and multiply by 100 to get units on a U-100 syringe. The whole conversion is one division and one multiplication; the only thing that makes it feel hard is that the first number is specific to your vial and nobody else can supply it.

Question 2

How many units is 1 mL?

Accepted Answer

100 units on a U-100 syringe, 40 units on a U-40 veterinary syringe, and 500 units on a U-500 syringe. The U number is literally units per millilitre. Every human insulin syringe sold in the US is U-100 except the dedicated U-500 barrel cleared for U-500 insulin, and ISO 8537 is the standard those scales are built against.

Question 3

Is a unit always 0.01 mL?

Accepted Answer

Only on a U-100 barrel. On a U-40 barrel a unit is 0.025 mL and on a U-500 barrel it is 0.002 mL. That is why the barrel type matters more than any number on this page: the same figure drawn on the wrong scale is off by a factor of 2.5 in one direction or 5 in the other, and both errors are documented in the published case literature.

Question 4

Why does every site give a different answer for the same dose?

Accepted Answer

Because each has silently assumed a concentration. A page that tells you 5 mg is 50 units has assumed 10 mg/mL; a page that says 25 units has assumed 20 mg/mL. Both are arithmetically correct for their own assumption and neither knows your vial. That is the whole reason this cluster of pages leads with the concentration question instead of answering past it.

Question 5

Does the type of peptide change the conversion?

Accepted Answer

No. The arithmetic is identical for every compound, because it is about volume and mass rather than pharmacology — a milligram of tirzepatide and a milligram of BPC-157 occupy the same place on the syringe at the same concentration. What differs between compounds is which doses are appropriate, which is a question about the drug and not about the conversion.

Concentration	Example vial + water	2.5 mg is
1 mg/mL	2 mg in 2 mL	250 units
2 mg/mL	4 mg in 2 mL	125 units
2.5 mg/mL	5 mg in 2 mL	100 units
5 mg/mL	10 mg in 2 mL	50 units
10 mg/mL	20 mg in 2 mL	25 units
20 mg/mL	40 mg in 2 mL	12.5 units

Concentration	A vial that gives it	Units per mg	mg per unit
2.5 mg/mL	5 mg vial + 2 mL	40	0.025
5 mg/mL	10 mg vial + 2 mL	20	0.05
6.67 mg/mL	10 mg vial + 1.5 mL	15	0.067
10 mg/mL	30 mg vial + 3 mL	10	0.1
12.5 mg/mL	25 mg vial + 2 mL	8	0.125
15 mg/mL	30 mg vial + 2 mL	6.67	0.15
20 mg/mL	60 mg vial + 3 mL	5	0.2
30 mg/mL	60 mg vial + 2 mL	3.33	0.3

mg to Units Converter (and Units to mg)

Convert from your concentration

Why there is no single answer

The one table that answers every version of this question

The scale on the barrel matters more than the number

Milligrams to units

Units to milligrams

Tirzepatide

Micrograms, millilitres and IU

Common questions

Sources

Barrel	Units per mL	One unit is	Printed steps
0.3 mL "30 unit" (U-100)	100	0.01 mL	1
0.3 mL half-unit (U-100)	100	0.01 mL	0.5
0.5 mL "50 unit" (U-100)	100	0.01 mL	1
1 mL "100 unit" (U-100)	100	0.01 mL	2
1 mL U-40 (veterinary)	40	0.025 mL	1
1 mL U-500	500	0.002 mL	1