Peptide labels mix milligrams, micrograms, milliliters, syringe “units,” and sometimes international units (IU). Most mistakes happen when these get confused. This guide explains what each one means and walks through the math step by step. It covers math only, not doses.
Key takeaways
- Concentration = mg in vial ÷ mL of liquid.
- On a U-100 syringe, 100 units = 1 mL. Units measure volume, not strength.
- In a blend, each draw splits by each ingredient’s share of the vial.
- IU and syringe units are not the same thing.
- This is math, not dosing guidance.
Mass vs volume
Milligrams (mg) and micrograms (mcg) describe how much compound is present: 1 mg = 1,000 mcg. Milliliters (mL) describe how much liquid there is. A vial labeled “10 mg” holds 10 mg of powder, no matter how much liquid goes into it.
Step 1: Find the concentration
Divide the amount in the vial by the liquid volume: mg ÷ mL = mg/mL. A 10 mg vial mixed with 2 mL of liquid gives 5 mg/mL. Mixed with 1 mL, the same vial gives 10 mg/mL.
Step 2: Convert an amount to syringe units
A U-100 syringe is marked so that 100 units = 1 mL. To find how many units hold a given amount: (amount ÷ concentration) × 100. At 5 mg/mL, 0.5 mg is (0.5 ÷ 5) × 100 = 10 units.
Step 3: Count portions and check the clock
Divide the vial amount by the portion size to see how many portions a vial holds. Remember that many references limit a mixed, multi-use vial to about 28 days, so a vial can hold more portions on paper than can be used in that window.
Blends: one draw, several compounds
In a pre-mixed blend, every draw contains every ingredient in a fixed ratio. Add up all ingredients to get the total concentration, then split each draw by each ingredient’s share. For example, a 70 mg blend listed as GHK-Cu 50 mg + BPC-157 10 mg + TB-500 10 mg, mixed with 3 mL, is 23.33 mg/mL. So 10 units holds about 2.33 mg total: about 1.67 mg GHK-Cu and 0.33 mg each of BPC-157 and TB-500. If a label shows only a blend name and a total, this math can’t be done.
IU and liquid vials
IU work the same way (10,000 IU in 10 mL = 1,000 IU/mL), but IU measure biological activity and have no universal mg conversion. Pre-mixed liquid vials such as vitamin B12 need no mixing. Read the printed concentration, because 1,000 mcg/mL and 5,000 mcg/mL lots differ by 5×.
The mistakes to avoid
- Confusing mg and mcg (a 1,000× error)
- Treating syringe units as IU
- Using a chart made for a different vial size or mixing volume
- Reading a blend total as the amount of each ingredient
- Rounding very small volumes. Rounding 2.5 units to 3 is a 20% change.
Try the calculators on our Peptide Math page, including the new blend calculator. For how doses are actually set, see where dosing numbers come from.
Medical disclaimer: Pep Guide is for educational purposes only. It is not medical advice, diagnosis or treatment. Research changes over time. Talk to a licensed healthcare provider before starting, stopping or changing any medication or compound.