Home / Guides / Peptide reconstitution: how many units to draw

The three numbers you need

1. Vial size: how many milligrams of peptide are in the vial (printed on the label)
2. Water added: how many millilitres of bacteriostatic water you add when reconstituting
3. Your prescribed dose: the amount your prescriber told you to take, in mg or mcg

A worked example

Say you have a 5 mg vial and you add 2 mL of bacteriostatic water:

• Concentration: 5 mg divided by 2 mL = 2.5 mg/mL
• Prescribed dose: 0.25 mg (250 mcg)
• Volume needed: 0.25 divided by 2.5 = 0.1 mL
• On a U-100 insulin syringe, 1 mL = 100 units, so 0.1 mL = 10 units

Adding more water spreads the same vial across more units, which makes small doses easier to measure accurately. Adding less concentrates it into fewer units. The dose itself never changes; only the volume you draw does.

Where napkin maths goes wrong

The mistakes are always the same: mixing up mg and mcg (a thousand-fold error), forgetting how much water went into this particular vial, and re-doing the calculation from memory three weeks later after the numbers have faded. A calculation you do once, correctly, at reconstitution time is safe territory; a calculation re-derived from memory on a tired evening is not.

How PepLevel handles it

In PepLevel each vial is saved as a supply: how much peptide it holds and how much water you added. From then on the app shows your next planned dose as a volume in mL, and as syringe units too if you enter your syringe's scale, next to the dose on Today, on the medication page and when you log. It also tracks how much is left in the vial. It only converts the dose your prescriber set into a volume; it never works out what your dose should be.

No more napkin maths

Reconstitution and draw amounts, worked out for you and remembered per vial. Coming soon to the App Store.

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