The reconstitution formula
Every reconstitution problem comes down to one relationship: concentration = amount ÷ volume. Once you know the concentration, any dose can be turned into a volume, and any volume into a dose.
Concentration = amount of powder ÷ volume of diluent
Volume for a dose = dose ÷ concentration
Units (U-100) = volume in mL × 100
Example: 10 mg of powder in 5 mL gives 2 mg/mL. A 2 mg dose is then 2 ÷ 2 = 1 mL, which is 100 units on a U-100 syringe.
Working with different units
| Unit | Equals |
|---|---|
| 1 gram (g) | 1,000 milligrams (mg) |
| 1 milligram (mg) | 1,000 micrograms (mcg or µg) |
| 1 milliliter (mL) | 1 cubic centimeter (cc), 100 units on a U-100 syringe |
| 1 unit (U-100 syringe) | 0.01 mL |
Products measured in international units (IU) cannot be converted to mg with a general formula, because an IU is a measure of biological activity that differs from substance to substance. For those, work in IU throughout: concentration in IU per mL, dose in IU.
Displacement volume
When some powders dissolve, the final solution is slightly larger than the volume of diluent added. Pharmaceutical labels account for this, often by telling you to add a specific volume to reach a stated final concentration. If a product's instructions give a concentration after mixing, use that figure instead of calculating it.
For peptides mixed with bacteriostatic water, the peptide reconstitution calculator uses the same math with labels for vials and syringes, and the BAC water calculator chooses a water volume for you.
Reconstitution questions
What is reconstitution?
Reconstitution means dissolving a dry powder (often freeze-dried, or lyophilized) in a liquid, called the diluent, to make a solution of a known strength. Many medicines, vaccines, research reagents and peptides are supplied this way because the powder is more stable than the liquid.
How do I calculate the concentration after reconstitution?
Divide the amount of powder by the volume of diluent: concentration = amount ÷ volume. For example, 500 mg in 10 mL is 50 mg/mL. The calculator also turns a desired dose into a volume and syringe units.
Does the powder add volume?
Some powders add a noticeable volume when dissolved, called displacement volume, so the final volume is slightly more than the diluent you added. Pharmaceutical products state this in their instructions and often tell you exactly how much diluent to use. For small peptide vials the effect is usually tiny, but the product's instructions always take priority.
Which diluent should I use?
Use the one specified for the product: bacteriostatic water, sterile water, sodium chloride 0.9% or a supplied diluent. The choice affects stability and how long the solution can be kept.