Dosage
How to Calculate Peptide Dosage
Peptide dosing comes down to two questions: how concentrated is your vial after mixing, and how much liquid do you draw to get your dose? Here's the formula, step by step, with examples.
The two-step formula
Once a peptide is reconstituted (mixed with bacteriostatic water), every dose calculation uses the same two steps.
2. Volume to draw (mL) = desired dose (mg) ÷ concentration (mg/mL)
That's it. The first step is fixed the moment you mix the vial; the second step you repeat for each dose. To read the result on an insulin syringe, multiply the volume by your syringe's units-per-mL (100 for a U-100 syringe).
Step by step
- Note the peptide amount. This is printed on the vial, in milligrams (mg). For example, a 5 mg vial.
- Note how much water you added. The bacteriostatic water volume in milliliters (mL). For example, 2 mL.
- Find the concentration. Divide: 5 mg ÷ 2 mL = 2.5 mg/mL.
- Convert your dose to the same units. If your dose is in micrograms (mcg), divide by 1,000 to get mg (250 mcg = 0.25 mg).
- Find the volume to draw. Divide: 0.25 mg ÷ 2.5 mg/mL = 0.1 mL.
- Convert to syringe units. On a U-100 syringe, 0.1 mL × 100 = 10 units.
Worked example
Say you have a 5 mg vial, you reconstitute it with 2 mL of bacteriostatic water, and you want a 250 mcg dose using a U-100 syringe:
Dose = 250 mcg = 0.25 mg
Volume to draw = 0.25 mg ÷ 2.5 mg/mL = 0.1 mL
Units (U-100) = 0.1 mL × 100 = 10 units
So you'd draw to the 10-unit mark. Change the water volume and the result changes: mix the same 5 mg vial with 1 mL instead, and the concentration doubles to 5 mg/mL, so the same 250 mcg dose is only 0.05 mL, or 5 units.
Don't want to do the math?
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Open the free calculatormcg vs mg
Peptide doses are often written in micrograms and vials in milligrams, so keep the conversion handy:
Always convert both your dose and your vial amount to the same unit before dividing, or the result will be off by a factor of 1,000.
Common mistakes
- Mixing units. Dividing a dose in mcg by a concentration in mg/mL without converting first.
- Confusing mL and units. Volume to draw is in mL; the syringe shows units. They are not the same number unless you multiply by the syringe's units-per-mL.
- Assuming all syringes match. A U-40 syringe reads differently than a U-100. See the guide below.
This guide is for calculation and educational purposes only and is not medical advice. It does not recommend any peptide, dose, or protocol. Always consult a qualified clinician before starting, changing, or stopping any peptide.