Bacteriostatic Water Calculator
Tell us your vial size and target dose — we'll show you how much bacteriostatic water to add for clean, round syringe marks.
Suggested BAC Water Volumes
Pick the option where the "Units Per Dose" lands on a round, easy-to-read mark on your syringe.
| BAC Water | Units Per Dose | Concentration | Doses Per Vial |
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Create Free AccountHow Much Bacteriostatic Water Should I Add?
There's no single "correct" amount of BAC water for a peptide vial. Any reasonable volume (typically 1–5 mL) will fully dissolve the powder. The choice is about what makes your syringe math easy.
The Rule of Thumb
Add enough water so your typical dose lands on a round mark — commonly 10, 20, 25, or 50 units on a U-100 insulin syringe. This makes daily dosing fast and reduces the chance of a measurement error.
Why Not Always 1 mL?
1mL minimizes injection volume (more comfortable) and extends shelf-life for peptides sensitive to repeated freeze-thaw. But it often produces awkward numbers — for a 5mg BPC-157 vial in 1mL of water, a 250mcg dose = 5 units, which is a very small volume to draw accurately. 2mL gives 10 units, which is easier to measure.
Why Not 5+ mL?
Very dilute solutions require larger injection volumes (e.g. 30+ units = 0.3mL). That's more liquid under the skin per dose, and if your vial only holds ~5mL total you have less headroom.
GLP-1 Peptides Are Different
Semaglutide and tirzepatide have high milligram doses and weekly schedules, so common reconstitution volumes are 1–2mL. The goal here is slightly different: you want to minimize injection volume (weekly sub-Q shots) and keep the math aligned with known titration steps (0.25mg, 0.5mg, 1mg, 1.7mg, 2.4mg).