How to Calculate Peptide Doses: Reconstitution Math, IU Conversions, and Syringe Marks

The three variables

Every peptide dose calculation comes down to three numbers:

• Vial size — the amount of dry peptide in the vial. Typically labeled in milligrams (mg). A 5 mg vial contains 5 mg of peptide.
• Reconstitution volume — the amount of bacteriostatic water added. Typically a round number like 1 mL, 2 mL, 3 mL, or 5 mL. You choose this when you reconstitute.
• Target dose — the amount of peptide you want to deliver in each injection. Typically expressed in micrograms (mcg) or milligrams (mg).

Two derived numbers connect them: concentration (peptide per volume) and dose volume (how much of that solution contains your dose).

The core formula

The math is two steps.

Step 1: concentration = vial size / reconstitution volume. A 5 mg vial in 1 mL gives 5 mg/mL. A 10 mg vial in 2 mL gives 5 mg/mL. A 5 mg vial in 5 mL gives 1 mg/mL. More water means lower concentration — and a larger volume per dose.

Step 2: dose volume = target dose / concentration. If your concentration is 5 mg/mL (5,000 mcg/mL) and you want 250 mcg, the dose volume is 250 / 5,000 = 0.05 mL.

That is the entire calculation. Everything else is unit conversion.

Insulin syringes and the IU convention

Insulin syringes are marked in International Units (IU), not in milliliters. The conversion is fixed and dictated by insulin's standard concentration:

100 IU = 1 mL

Or equivalently, 1 IU = 0.01 mL. This is purely a labeling convention — IU on an insulin syringe is a volume marking, not a measure of the substance inside. A 100 IU insulin syringe holds 1 mL total.

So once you know your dose volume in mL, multiply by 100 to get IU: a 0.05 mL dose is 5 IU on the syringe. A 0.10 mL dose is 10 IU. A 0.20 mL dose is 20 IU. The syringe markings are where the math finally lands.

Worked examples

Example 1: BPC-157, 250 mcg dose. Vial is 5 mg, reconstituted in 2 mL bacteriostatic water.

• Concentration: 5 mg / 2 mL = 2.5 mg/mL = 2,500 mcg/mL
• Dose volume: 250 mcg / 2,500 mcg/mL = 0.1 mL
• Syringe mark: 0.1 mL = 10 IU

Example 2: Ipamorelin, 200 mcg dose. Vial is 5 mg, reconstituted in 1 mL.

• Concentration: 5 mg / 1 mL = 5 mg/mL = 5,000 mcg/mL
• Dose volume: 200 / 5,000 = 0.04 mL
• Syringe mark: 0.04 mL = 4 IU

Example 3: TB-500, 2.5 mg dose. Vial is 10 mg, reconstituted in 5 mL.

• Concentration: 10 mg / 5 mL = 2 mg/mL
• Dose volume: 2.5 mg / 2 mg/mL = 1.25 mL
• Syringe mark: 1.25 mL is too much for an insulin syringe — would need a larger syringe (e.g., a 1 mL or 3 mL tuberculin syringe).

Example 3 illustrates a useful design principle: choose reconstitution volume to make doses land at convenient syringe marks. Reconstituting the 10 mg TB-500 vial in 2 mL instead would give 5 mg/mL — making 2.5 mg = 0.5 mL = 50 IU, which fits comfortably on a 100 IU insulin syringe.

Common mistakes

Mixing up mcg and mg. 1 mg = 1,000 mcg. A protocol that says "250 mcg" is one-quarter the amount of one that says "250 mg" — by a factor of 1,000. Always confirm the unit before doing the math.

Confusing IU with units of the drug. IU on an insulin syringe is a volume measurement (1 IU = 0.01 mL). It is not a measure of the peptide itself. The peptide content of an IU depends entirely on the concentration in your reconstituted vial. Same syringe mark, two different peptides, two different actual peptide amounts.

Using insulin-conversion shortcuts. Some community guides offer "easy" lookup tables that assume specific reconstitution volumes. These are fine if the reconstitution matches; if it doesn't, the table is wrong. Better to do the math once for your specific reconstitution and use that.

Forgetting to recalculate when changing vial sizes. If you switch from a 5 mg to a 10 mg vial and keep the same reconstitution volume, your concentration doubles — and your IU per dose halves. Same dose, half the syringe volume.

Net peptide content: when the math is off

One subtlety: the vial label is the total dry mass, which usually includes counterions, residual water, and other non-peptide material. The actual peptide mass — net peptide content — is typically 70-90% of the label. A "5 mg" vial may contain 4-4.5 mg of actual peptide.

For most research-peptide use this discrepancy is absorbed into the imprecision of community-grade dosing protocols (which are typically rounded to convenient numbers anyway). For research or clinical work where exact dose matters, the net peptide content from a Certificate of Analysis is the number to use, not the label. See the COA guide for how to read that information.

The honest read

Reconstitution math is not difficult — it is concentration and a unit conversion. The reason it feels confusing in community guides is that different sources use different unit conventions (mcg vs mg, IU vs mL, label mass vs net mass) without flagging the differences. Doing the math from first principles once for your specific vial and reconstitution volume is faster, less error-prone, and more flexible than relying on lookup tables. The formula is simple enough to do on a napkin: concentration = mg/mL; dose volume = mcg / (concentration in mcg/mL); IU = dose volume × 100.