Peptide dosing maths: mg, mcg, IU and insulin syringe units

1 mg is 1,000 mcg, and a standard 1 ml insulin syringe has 100 units, so 1 unit is 0.01 ml. To turn a dose into syringe units, work out the concentration (mcg per ml), then divide by 100 to get mcg per unit.

This article is about arithmetic, not about what anyone should take. Most of these compounds are unlicensed research chemicals, and the doses on this site are descriptions of what people report, not recommendations or medical advice.

The units, in plain English

• mg (milligram): one thousandth of a gram. Vials are usually labelled in mg
• mcg or µg (microgram): one thousandth of a milligram. Doses of many peptides are in mcg
• ml (millilitre): a volume of liquid
• IU (international unit): a measure of biological activity, not weight. Used for things like hCG and growth hormone
• Insulin syringe units: markings on the syringe, not a measure of drug. On a 1 ml (U-100) syringe, 100 units = 1 ml

Conversion table, in list form

• 1 mg = 1,000 mcg
• 0.1 mg = 100 mcg
• 0.25 mg = 250 mcg
• 1 ml = 100 units (U-100 syringe)
• 10 units = 0.1 ml
• 50 units = 0.5 ml
• Half-size syringes (0.5 ml, 50-unit) have the same markings per unit but hold less. Always confirm which syringe you have

The four-step method

1. Vial amount in mcg: multiply mg by 1,000
2. Concentration in mcg per ml: divide by the ml of water you added
3. mcg per unit: divide the concentration by 100
4. Units for a dose: divide the dose in mcg by mcg per unit

Worked example 1: 5 mg vial, 2 ml of water

• 5 mg = 5,000 mcg
• 5,000 / 2 ml = 2,500 mcg per ml
• 2,500 / 100 = 25 mcg per unit
• A 250 mcg dose = 250 / 25 = 10 units

That is the example used on the BPC-157 page, and it also fits ipamorelin, where a 100 mcg dose is 4 units with the same mix.

Worked example 2: change the water, change the units

Same 5 mg vial, but 1 ml of water:

• 5,000 / 1 ml = 5,000 mcg per ml
• 5,000 / 100 = 50 mcg per unit
• A 250 mcg dose = 250 / 50 = 5 units

Same peptide, same dose, but the syringe reading halves. This is why a dose "in units" is meaningless unless you also know the vial size and water volume.

Worked example 3: a 10 mg vial, 2 ml of water

• 10 mg = 10,000 mcg
• 10,000 / 2 = 5,000 mcg per ml
• 5,000 / 100 = 50 mcg per unit
• A 2.5 mg dose = 2,500 mcg = 2,500 / 50 = 50 units

The semaglutide page uses the same method with a 5 mg vial in 2 ml: 2.5 mg/ml, so a 0.25 mg starter dose is 10 units.

Worked example 4: IU products

For something sold in IU, such as a vial of hCG, the logic is the same but you start from IU rather than mg. Suppose a vial contains 5,000 IU and you add 5 ml of water:

• 5,000 IU / 5 ml = 1,000 IU per ml
• 1,000 / 100 = 10 IU per syringe unit
• A 250 IU dose = 250 / 10 = 25 units

For growth hormone, vials are often labelled in both mg and IU, and conversion factors are quoted by manufacturers, commonly around 3 IU per mg. Do not rely on a rule of thumb. Use the figure printed on your own product, and if it does not say, treat the dose as uncertain. See the HGH page for more context.

Common mistakes

1. Mixing up mg and mcg

A 1,000-fold slip. 0.25 mg is 250 mcg, not 25 mcg and not 2,500 mcg.

2. A misplaced decimal point (the 10x error)

The most dangerous mistake is a tenfold one: reading 2.5 mg as 25 mg, or 10 units as 100 units. Defences:

• Write the full calculation down every time you change the vial or the water volume
• Do a sense check: a 5 mg vial can only hold 5,000 mcg in total, so a 250 mcg dose should be a small fraction (1/20th) of the liquid, not half of it
• Calculate in a second way, such as in ml, and check you get the same answer

3. Assuming the "units" quoted online apply to you

A forum post saying "10 units" is meaningful only for that person's vial size and water volume. Always re-derive from the mg and ml you actually have.

4. Wrong syringe

A 0.5 ml or 0.3 ml insulin syringe is marked differently from the 1 ml one in terms of what a full barrel holds. A U-40 syringe (sometimes used for veterinary insulin) has a different scale, with 40 units per ml, and would give a very different volume. Check the pack.

5. Forgetting a blend has two compounds

In a combined vial such as CJC-1295 with ipamorelin, the vial's mg may be split between two peptides. Read the label for the amount of each before you calculate.

6. Not counting the dead space

Some syringes hold a little liquid in the needle hub. This matters more with very small volumes, and it is another reason why using a larger volume of water makes dosing more consistent.

Strength vs. volume: a useful way to think

Adding more water does not change how much peptide is in the vial. It only changes how that peptide is spread through the liquid. Weaker mixes give larger, easier-to-read volumes, which helps accuracy with tiny doses, for instance with potent products such as IGF-1 LR3, where doses are very small. Our reconstitution guide covers the mixing steps.

Bottom line

The maths is only multiplication and division, but small slips become large errors. Always work from your own vial's mg and your own water volume, write it down, and sense-check the answer. If the numbers do not feel right, stop and recalculate. More on keeping risks down is on the safer use page.