How to calculate concentration after reconstitution — a calculator guide

After reconstituting a lyophilizate, the concentration of the solution depends on two numbers: the amount of material in the vial and the volume of solvent added. The maths is simple, but easy to get wrong — which is why it is worth calculating rather than guessing.

The basic formula

Concentration = mass of material ÷ volume of solvent. If you have 5 mg of material and add 2 ml of bacteriostatic water, you obtain a solution at 2.5 mg/ml. Adding 1 ml instead of 2 ml gives 5 mg/ml — the less water, the more concentrated the solution.

Worked examples

• 10 mg + 2 ml → 5 mg/ml
• 5 mg + 1 ml → 5 mg/ml
• 2 mg + 2 ml → 1 mg/ml

Note that different combinations can give the same concentration — what matters is the ratio of mass to volume.

Ready-made calculator

Instead of working it out by hand, use our reconstitution calculator — you enter the mass of material and the volume of water, and the tool returns the concentration of the solution. It removes arithmetic slips and speeds up the work.

Good practice

Add the water slowly down the wall of the vial, without vigorous mixing. Store the solution in a refrigerator and use it within roughly 4 weeks. More on this: how to store peptides.

Materials for research purposes only. Not for human or animal consumption. We do not advise on use.