Updated October 8, 2026

Peptide Reconstitution Calculator: How the Math Works (With Examples)

Reconstitution math is where most tracking mistakes happen. The formula itself is simple — the errors come from unit conversions (mg vs mcg) and from translating a volume into marks on an insulin syringe. This guide walks through the math step by step, with worked examples, so you can sanity-check any calculator — including ours.

Note: this article explains arithmetic only. It does not recommend doses, compounds, or protocols. Your amounts come from you and your licensed healthcare provider.

Step 1: Concentration

When you add bacteriostatic (BAC) water to a lyophilized vial:

concentration (mg/mL) = vial amount (mg) ÷ BAC water added (mL)

Example: a 5 mg vial + 2 mL of BAC water → 5 ÷ 2 = 2.5 mg/mL (which is 2,500 mcg/mL).

Step 2: Volume per dose

volume (mL) = dose (mg) ÷ concentration (mg/mL)

Example: a 0.25 mg dose at 2.5 mg/mL → 0.25 ÷ 2.5 = 0.1 mL.

Step 3: Convert volume to insulin syringe units

Insulin syringes are marked in "units" where 100 units = 1 mL (U-100):

units = volume (mL) × 100

So 0.1 mL = 10 units on a U-100 syringe. On a 30-unit or 50-unit syringe the scale is the same — the barrel is just smaller, so the marks are further apart and easier to read for small volumes.

The three mistakes that cause most errors

1. mg/mcg confusion. 1 mg = 1,000 mcg. A dose written in mcg divided by a concentration in mg/mL without converting gives an answer off by 1,000×. Always convert to the same unit first.
2. "Units" ≠ dose. Syringe units measure volume, not compound. 10 units of a 2.5 mg/mL solution and 10 units of a 5 mg/mL solution contain different amounts. If you change how much water you add, your draw changes too.
3. Losing track of reconstitution dates. Reconstituted peptides don't last forever. If you don't log the date you mixed a vial, you're guessing at freshness weeks later.

Worked example, end to end

• Vial: 10 mg. BAC water added: 3 mL.
• Concentration: 10 ÷ 3 = 3.33 mg/mL.
• Desired dose: 500 mcg = 0.5 mg.
• Volume: 0.5 ÷ 3.33 = 0.15 mL.
• Syringe: 0.15 × 100 = 15 units on a U-100 syringe.

Or skip the math entirely

PepMinder (free on Android) does all of the above in one screen: enter vial size, water volume, and dose, and it shows mg/mL, mcg/mL, units to draw, and a visual syringe diagram with the fill line marked for 30, 50, and 100-unit syringes. It also logs when you reconstituted each vial and flags vials that are expiring — the two things a plain calculator can't do.

Everything stays on your device: no account, no cloud.

PepMinder is a personal tracking and calculation tool. It does not provide medical advice, diagnosis, dosing recommendations, or protocols, and it does not sell or link to any products. Always consult a licensed healthcare provider about your treatment.