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Dilution Calculator in mL - How Much Liquid to Add

A dilution calculator in mL answers: how many mL do I need to get the concentration I want, and how many mL do I draw for my dose?

It all starts with what’s in your vial.

1. Find your concentration after mixing:

Concentration (mg/mL) = Total mg in vial / mL of bacteriostatic water you add

Example: 10 mg vial + 2 mL water = 5 mg/mL

Same vial + 1 mL water = 10 mg/mL

More mL = lower concentration, easier to measure. Less mL = higher concentration, tiny volumes.

2. Find mL for your dose:

mL needed = Desired dose (mg) / Concentration (mg/mL)

Example: You want 0.25 mg from that 5 mg/mL vial.

0.25 / 5 = 0.05 mL

On a U-100 insulin syringe, 1 mL = 100 units, so 0.05 mL = 5 units.

3. If you already have a liquid and want to dilute it further:

Use C1 x V1 = C2 x V2

C1 = current mg/mL, V1 = current mL, C2 = target mg/mL, V2 = final mL you want.

If you have 1 mL at 10 mg/mL and you want 5 mg/mL, you need a final volume of 2 mL — so add 1 mL more diluent.

Label your vial with final mg/mL and mixing date, keep it refrigerated, and have your pharmacist or prescriber double-check your math before use.