Peptide Reconstitution Calculator: How to Do the Math Correctly
Reconstituting a peptide is straightforward math, but it's where the most dose errors happen. Here's the formula, the common mistakes, and a built-in calculator that does it for you.
The basic math
Three numbers matter:
- Vial size: the lyophilized (powder) amount, in mg
- BAC water added: the volume of bacteriostatic water you reconstitute with, in ml
- Target dose: how much you want to draw, in mcg
The formula:
- Concentration = (vial mg × 1000) / BAC ml = mcg per ml
- Concentration / 100 = mcg per "unit" on a U-100 syringe
- Target dose / mcg per unit = units to draw
Worked example: BPC-157
5 mg BPC-157 vial + 2 ml BAC water:
- Concentration = (5 × 1000) / 2 = 2500 mcg/ml
- Per U-100 unit = 2500 / 100 = 25 mcg
- For a 250 mcg dose: 250 / 25 = 10 units
Worked example: semaglutide
5 mg semaglutide vial + 2 ml BAC water:
- Concentration = 2500 mcg/ml = 2.5 mg/ml
- For a 0.25 mg starter dose: 0.25 / 2.5 = 0.1 ml = 10 units
- For a 0.5 mg dose: 20 units
Use our free calculator
Skip the math: our reconstitution calculator takes vial + BAC water + target dose and gives you the exact units in real time. No app required. No data sent anywhere.
Common mistakes
- Confusing mg with mcg. Semaglutide is dosed in mg, BPC-157 in mcg. Don't mix them up — a 1000x error.
- Wrong syringe scale. U-100 syringes are most common. U-40 (less common) read differently. Always confirm.
- Forgetting to recalc when vial changes. If you switch from a 5 mg to a 10 mg vial, your math changes.
- Dead space in syringe. Insulin syringes lose ~3-5 units in dead space. Negligible at high doses, meaningful at micro-doses.