Concentration = peptide mg ÷ diluent mL. Divide your target amount by that concentration to get the volume in mL, then multiply mL × 100 for units on a U-100 syringe.
Reconstitution math is not complicated, but it is unforgiving. A single slip, the wrong diluent volume, a misplaced decimal, the wrong syringe scale, quietly changes every number downstream. For anyone keeping research logs, the goal is not just getting a number; it is getting a number you can show your work for later. This walkthrough breaks the chain into four clean steps.
Step 1, The one formula everything rests on
Concentration is simply how much peptide is dissolved in how much liquid:
Concentration (mg/mL) = peptide amount (mg) ÷ diluent volume (mL)
If a vial is labeled 5 mg and you add 2 mL of diluent, the concentration is 2.5 mg/mL. Add 1 mL instead and the same 5 mg becomes 5 mg/mL. The peptide amount never changed, only how concentrated it is.
Step 2, From concentration to a draw volume
Once you know the concentration, the volume needed for any target amount is:
Volume (mL) = target amount (mg) ÷ concentration (mg/mL)
Using an illustrative target of 0.25 mg (250 mcg) at 2.5 mg/mL: 0.25 ÷ 2.5 = 0.10 mL. Note the unit trap here, targets are often written in micrograms while concentration is in mg/mL. There are 1,000 mcg in 1 mg, so convert before you divide.
Step 3, From milliliters to syringe units
A volume in milliliters still has to be read off a syringe, and most are marked in units, not mL. On a standard U-100 insulin syringe, 100 units = 1 mL, so each unit is 0.01 mL. That makes the conversion a simple ×100:
Units = volume (mL) × 100
Our 0.10 mL becomes 10 units, “draw to the 10 mark.” This is exactly where readings go wrong, so it is worth its own guide on reading units on an insulin syringe.
Step 4, What to record so it is auditable
The number on the syringe is the least interesting part of the log. What makes an entry reviewable is the inputs behind it. A complete reconstitution record captures:
- Peptide amount as written on the label (mg)
- Diluent type and volume added (mL)
- The resulting concentration (mg/mL)
- The target amount used for the calculation
- The computed volume (mL) and units
- The syringe scale you actually used
- Date reconstituted
If any field is unknown, mark it unknown rather than guessing, a log that admits a gap is more trustworthy than one that hides it. The diluent you choose also affects how long the vial stays usable, which is covered in BAC water vs. sterile water.
Why a calculator beats mental math
None of these steps is hard in isolation. The errors come from doing them in sequence, under time pressure, with unit conversions in between. PepSync’s reconstitution calculator locks the chain together, so the units on your syringe always trace back to the mg on your label, and every input is captured in the same place for later review.
Frequently asked questions
How do you calculate peptide reconstitution concentration?
Divide the peptide amount in milligrams by the volume of diluent in milliliters. For example, 5 mg dissolved in 2 mL gives a concentration of 2.5 mg/mL.
How do you convert milliliters to insulin units?
On a U-100 syringe, multiply the volume in mL by 100. So 0.10 mL equals 10 units, and 0.20 mL equals 20 units.
How many micrograms are in a milligram?
There are 1,000 micrograms (mcg) in 1 milligram (mg). Convert a target written in mcg to mg before dividing by a concentration in mg/mL.