Peptide Calculator Guide — How to Use It Right

The Core Concept

Why BAC Water Is the Variable That Matters

Vial size is fixed — it's printed on the vial and can't be changed. Your dose is determined by your protocol. The only input you control is how much bacteriostatic water you add. That single decision sets the concentration of your solution, which determines the syringe draw for every injection from that vial. Change the BAC water amount and every draw changes.

The calculation: concentration (mcg/mL) = vial size in mcg ÷ BAC water in mL. For a 5mg (5,000mcg) vial + 2mL BAC water: 5,000 ÷ 2 = 2,500 mcg/mL. Your draw units = (dose ÷ concentration) × 100. For 250mcg dose: (250 ÷ 2,500) × 100 = 10 units. That's the complete calculation.

The practical rule: Choose a BAC water volume that produces a draw in the 10–25 unit range at your dose. Sub-5-unit draws are hard to measure accurately on a standard U-100 syringe.

Custom Draw Mode

When You Want to Choose the Draw First

Custom Draw inverts the calculation. Instead of entering BAC water and getting draw units, you enter the draw units you want and get the BAC water amount. Useful when you've decided you want exactly 20 units per dose for readability — enter that target and the calculator gives you the BAC water volume to add when reconstituting.

Available in the calculator on this page and at reconstitution.health. No other free web peptide calculator has this mode.

FAQ

Common Questions

What happens if I add the wrong BAC water amount?

Every dose from that vial will be at the wrong concentration. If you added twice the BAC water you intended, your draw units are half what they should be — you're injecting half the dose. The solution is visually identical to a correct preparation. Always calculate before reconstituting and verify that the resulting draw units are reasonable for your compound and dose.

Can I add more BAC water to an already-reconstituted vial?

You could physically, but you shouldn't. Once you've reconstituted and taken draws from the vial, you can't know exactly how much BAC water was added vs what's been removed. Adding more changes the concentration unpredictably. Reconstitute fresh with the correct amount — don't correct a mis-reconstituted vial mid-cycle.

What is the difference between draw units and mL?

On a U-100 insulin syringe: 100 units = 1mL. 10 units = 0.1mL. 20 units = 0.2mL. The "units" scale is a convention from insulin dosing — 1 unit of U-100 insulin = 0.01mL. For peptide math, you can use either — the calculator gives you both. Draw to the unit marking on the syringe barrel, not to a mL measurement.

How to Use a Peptide Calculator Correctly

Why BAC Water Is the Variable That Matters

When You Want to Choose the Draw First

Common Questions

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