Reconstitution math is genuinely simple arithmetic that gets needlessly confusing because of how many different units show up at once — milligrams, milliliters, and international units, sometimes all in the same sentence. Once the units are untangled, the actual math is a single division problem.
The Only Formula You Need
Concentration is just total peptide mass divided by total liquid volume: milligrams of peptide, divided by milliliters of bacteriostatic water added, equals milligrams per milliliter. That's the entire calculation. Everything else — every online calculator, every chart — is just this same division, dressed up for different unit preferences.
Worked Example
Take a vial labeled 10mg. Add 2mL of bacteriostatic water. 10 divided by 2 gives you a concentration of 5mg/mL. That single number — 5mg per milliliter — is the only thing you need to know to figure out how much liquid corresponds to any given amount of peptide.
Why People Get Tripped Up by Syringe Units
Confusion usually starts when a syringe is marked in “units” (a scale left over from insulin syringes) rather than milliliters. The fix is a fixed conversion, not a new formula: a standard insulin syringe marks 100 units as equal to 1mL. So 50 units on that syringe is 0.5mL, and 20 units is 0.2mL — a straightforward proportion once you know that one reference point.
“It's one division problem wearing three different unit systems as a disguise.”
— a peptide researcher who reviews reconstitution questions in the community regularlyPutting the Two Steps Together
Once you have your concentration (mg/mL) from the first step, converting to syringe units for a specific amount is a second, equally simple division: divide the amount you want by your concentration to get the volume in mL, then multiply that volume by 100 to get units. Using the 5mg/mL example above, if you wanted to measure out 1mg, that's 1 divided by 5, or 0.2mL — which is 20 units on a standard insulin syringe.
A Few Things Worth Double-Checking
- Confirm your syringe's actual scale — not all syringes use the 100-units-per-mL insulin standard.
- Recheck the label's stated mg amount against the COA's measured quantity — they're not always identical, and the COA's measured figure is the more accurate one to calculate from.
- Redo the math from scratch for every new vial size rather than reusing a previous calculation — a different mg amount or a different water volume changes the concentration entirely.
None of this requires memorizing anything beyond the single division at the center of it. Everything past that is the same calculation, run twice, in whatever units the equipment in front of you happens to use.