The Peptide Calculator
That Works Backwards

What Custom Draw Does

Reverse Reconstitution — How It Works

Standard peptide reconstitution calculators take three inputs — vial size, BAC water volume, and target dose — and output the syringe draw units. You adapt your draw to whatever the calculation produces. Custom Draw inverts this: you specify the draw units you want per dose, and the calculator tells you exactly how much BAC water to add to your vial to produce that draw at your target dose.

The formula running in reverse: BAC water (mL) = Vial size (mcg) ÷ [(Draw units ÷ 100) × 1,000 ÷ Dose (mcg)]. In practice, you enter three things — vial size, dose, and target draw units — and get the exact BAC water volume. No spreadsheet required.

Custom Draw is available free at reconstitution.health and in the Protocol app on iOS and Android. As of June 2026, no other free or paid peptide calculator includes this mode.

Why It Matters

The Practical Value of Choosing Your Draw

On a U-100 insulin syringe, measurement precision degrades significantly below 5 units — the graduation marks are physically small and the plunger movement per unit is minimal. A 10-unit draw is readable. A 5-unit draw is manageable. A 3-unit draw is where errors accumulate. If your standard calculation gives you 7 units and you'd prefer 15 for accuracy, you previously had two options: accept 7 units, or recalculate manually until you found a BAC water volume that gave you a better draw. Custom Draw eliminates that iteration entirely.

For GLP-1 users running compounded semaglutide or tirzepatide, vial concentrations vary week to week during titration (2mg, 5mg, and 10mg vials are all common). Custom Draw means you can lock in your preferred draw unit and change nothing about your injection procedure as the vial size changes. The BAC water amount changes; the draw doesn't.

FAQ

Custom Draw Questions