About & methodology

Units to Draw is a free, single-purpose calculator. It turns three numbers you supply (the amount in a vial, the volume of diluent added, and the amount you want per draw) into a volume and a mark on an insulin syringe. It is math only, not medical advice. It does not recommend any compound, amount, schedule, or use, and it does not sell or link to any products.

Formulas

concentration (mcg/mL) = vial mg × 1000 ÷ water mL
volume (mL)            = amount mcg ÷ concentration
units                  = volume × scale   (U-100 = 100, U-50 = 50, U-40 = 40 units per mL)
draws per vial         = floor(vial mcg ÷ amount mcg)
reverse: water (mL)    = vial mg × 1000 × (target units ÷ scale) ÷ amount mcg
blend: total units     = sum of each vial's units

Conventions & checks

• 1 mg = 1,000 mcg. On a U-100 syringe, 1 unit = 0.01 mL.
• Results are shown to 1–3 decimals; we never round silently before computing.
• Draws under 5 units trigger a readability warning. A suggested water volume is shown only if it is 3 mL or less; otherwise we say no reasonable volume gets there.
• We warn when a draw exceeds the liquid in the vial or the syringe's capacity.
• The math is covered by automated unit tests, which run before every release.

Reference facts we rely on

• Bacteriostatic Water for Injection, USP: sterile water with 0.9% benzyl alcohol, supplied in multiple-dose vials (FDA label, DailyMed).
• Sterile Water for Injection, USP: no antimicrobial agent, single-dose containers (FDA label, DailyMed).
• Insulin syringe scales: U-100 = 100 units/mL; U-40 = 40 units/mL.

What this tool does not do

It doesn't tell you what to use, how much, or how often, and it doesn't assess whether substances can be mixed. Always verify numbers yourself and follow guidance from a licensed clinician or pharmacist.

Who runs it

Units to Draw is an independent project. It takes no money from peptide sellers. Questions or corrections: contact us.