Reconstitution math, without the spreadsheet
Every peptide reconstitution reduces to three numbers. Once those three make sense, the rest is arithmetic that fits on the back of a vial, and the calculator on your phone is a convenience, not a dependency.
Why the math trips people up
Most peptide users do the math wrong at least once. The mistakes are almost never complicated. They are almost always unit swaps: milligrams treated as micrograms, or the wrong syringe scale read as the right one. You are not bad at math if this has happened to you. You are running calculations in units your day job does not use, under lighting that was not designed for it, and the penalties for a slip compound quietly across a cycle.
A good mental model fixes this. Three numbers define the whole operation, and once they lock in, the rest is arithmetic that does not require a spreadsheet.
The three numbers
A lyophilised peptide is a dry powder in a sealed vial. To dose it, you add sterile bacteriostatic water (BAC water) and draw the resulting solution into an insulin syringe. Three inputs define every reconstitution:
Vial mass. Total peptide mass in the vial, printed on the label. Common sizes are 2 mg, 5 mg, and 10 mg.
BAC water volume. How much sterile diluent you add. More water means a weaker solution per unit on the syringe.
Target dose. What you want per injection. This is the one that is usually in micrograms, while the vial label is in milligrams. That gap is where most errors live.
The output is the number of units on a 1 mL U-100 insulin syringe. A U-100 syringe runs 100 units per mL, so every 10 units is 0.1 mL. Write that down somewhere you will see it before you draw.
The formula
units = (target dose mcg ÷ (vial mcg ÷ BAC mL)) × 100
In plain English: concentration is vial mcg divided by BAC mL. Dose divided by concentration is mL. Multiply by 100 to get units on a U-100 syringe. Always convert mg to mcg first (multiply by 1000). Do that conversion before you touch anything else.
Worked examples
Concentration: 5000 mcg ÷ 2 mL = 2500 mcg per mL. Dose volume: 250 ÷ 2500 = 0.1 mL. Syringe units: 10.
Target in mcg: 500. Concentration: 5000 ÷ 2.5 = 2000 mcg per mL. Dose volume: 500 ÷ 2000 = 0.25 mL. Syringe units: 25.
Concentration: 2000 ÷ 2 = 1000 mcg per mL. Dose volume: 100 ÷ 1000 = 0.1 mL. Syringe units: 10.
Concentration: 10000 ÷ 3 = 3333 mcg per mL. Dose volume: 200 ÷ 3333 = 0.06 mL. Syringe units: 6.
Where the errors come from
Unit swaps are the first and most expensive failure mode. A factor-of-1000 error in either direction turns a harmless dose into either a non-dose or an aggressive one. Write the units down.
The second mode is trusting the vial label under poor lighting. If the number is hand-written, verify twice. Third-party testing sometimes shows variance of roughly 10 percent between declared and measured mass, which matters when you are at the low end of a therapeutic window and are planning a cycle on the assumption that the label is exact.
The third is syringe confusion. Most insulin syringes sold in the US are U-100, but U-40 syringes exist, and using one when you planned for the other delivers roughly 2.5 times the peptide you intended. Check the printed scale on every new pack.
When to recalculate
Recalculate every time the vial size changes, every time you swap BAC water volume, and every time you change dose. If your target dose is stable and you are pulling from the same reconstitution, the units per dose do not change within that vial. Once you get to a fresh vial with a different reconstitution, the number almost always shifts.
Use the calculator
Pepture's reconstitution calculator runs this math for all 65 peptides in the library with pre-filled defaults. Change any field and the output updates. Inside the iOS and Android app, the same math runs on every dose entry, so the number you inject matches the number you logged.