Peptide unit converter
Three conversions that come up constantly in reconstitution work: microgram to milligram, International Units to milligrams, and millilitres to syringe units. All three run in your browser. None of them tell you what amount to use — they convert the numbers you already have.
Quick summary
- 1 mg = 1000 mcg. Mass conversion is fixed and works for every compound.
- IU is defined per substance. There is no universal IU-to-mg constant — you need that compound's own potency factor, which most research peptides do not have.
- 100 units = 1 mL on a U-100 syringe. Units measure volume, not the amount of compound in it.
Micrograms, milligrams and grams
The mass conversion is a straight factor of 1000 at each step, identical for every compound. This is the one you can apply without knowing what is in the vial.
| Micrograms | Milligrams |
|---|---|
| 50 mcg | 0.05 mg |
| 100 mcg | 0.1 mg |
| 250 mcg | 0.25 mg |
| 500 mcg | 0.5 mg |
| 750 mcg | 0.75 mg |
| 1000 mcg | 1 mg |
| 1500 mcg | 1.5 mg |
| 2500 mcg | 2.5 mg |
| 5000 mcg | 5 mg |
International Units and milligrams
An International Unit measures biological activity, not mass. The conversion between IU and mg is set separately for each substance, so there is no single formula — you have to supply the potency factor for the compound you are actually working with.
The factor defaults to 3 IU per mg, the long-standing convention for somatropin. It is correct for that and for nothing else by default — change it to your compound's own published factor, or do not use this block at all.
Millilitres and syringe units
A U-100 insulin syringe is graduated at 100 units per millilitre, so each unit is 0.01 mL. These markings describe volume only — the amount of compound in a given number of units depends on the concentration you mixed.
| Volume | U-100 units |
|---|---|
| 0.05 mL | 5 units |
| 0.1 mL | 10 units |
| 0.15 mL | 15 units |
| 0.2 mL | 20 units |
| 0.25 mL | 25 units |
| 0.3 mL | 30 units |
| 0.5 mL | 50 units |
| 0.75 mL | 75 units |
| 1.0 mL | 100 units |
A U-50 syringe uses the same 100 units-per-mL scale as a U-100 — it simply holds 0.5 mL, giving wider spacing between marks for small draws. A U-40 is a genuinely different scale and its markings do not mean the same thing.
Converting an amount into a draw
Unit conversion is only half the job. To turn a target amount into units on a syringe you also need the concentration in the vial, which is vial size divided by the bacteriostatic water you added. The reconstitution calculator does both steps at once and flags a draw that will not fit your syringe.
Unit conversion — frequently asked questions
How do I convert mcg to mg?
Divide by 1000. 1 mg = 1000 mcg, so 250 mcg is 0.25 mg and 1500 mcg is 1.5 mg. To go the other way, multiply mg by 1000.
How many mcg are in a mg?
Exactly 1000. The prefixes are fixed: a microgram is one thousandth of a milligram, and a milligram is one thousandth of a gram.
How do I convert IU to mg for a peptide?
You need the potency factor for that specific substance, because an International Unit is defined separately for each one. For somatropin the convention is roughly 3 IU per mg, so 6 IU is about 2 mg. That factor does not transfer to any other compound — most research peptides are measured in mg or mcg and have no IU definition at all.
Is there a universal IU to mg conversion?
No, and this is the most common mistake with unit conversion. IU measures biological activity, not mass, and the relationship between the two is set independently for each substance. Applying a growth-hormone factor to an unrelated peptide gives a meaningless number.
How many units is 0.25 mL on a U-100 syringe?
25 units. A U-100 syringe is graduated so that 100 units equals 1 mL, which makes every 0.01 mL one unit. This is a volume marking, not an amount of compound — how much compound those 25 units contain depends entirely on your concentration.
Do syringe units tell me how much peptide I have?
Not on their own. Units measure volume. To get the amount you also need the concentration, which is vial size divided by the bacteriostatic water you added. The reconstitution calculator does that step.
What is the difference between U-100, U-50 and U-40 syringes?
U-100 and U-50 are both graduated at 100 units per mL — a U-50 simply holds half a millilitre, so it has finer, easier-to-read spacing for small draws. A U-40 syringe is graduated at 40 units per mL, so its markings mean something different; do not read a U-40 as if it were U-100.
Is this medical advice?
No. This is a unit-conversion tool for education and research planning only. Compounds referenced are sold strictly as research chemicals and are not for human or veterinary use.
