Peptide calculator

Use this free peptide calculator to work out reconstitution volumes for research peptides. Enter the vial amount in milligrams and the volume of bacteriostatic water, and the calculator returns the concentration per unit for your laboratory records. For laboratory research use only.

Reconstitution: a handling and concentration guide

Reconstitution is simply dissolving a lyophilised (freeze-dried) powder into a liquid so that it can be measured, aliquoted and handled in the laboratory. It is a solution-preparation step and a concentration calculation. It is not a dose, and this guide does not describe any use in or on the body. These products are for research use only.

What reconstitution actually is

Peptides are shipped as a dry, lyophilised solid because that is their most stable form. To work with the material at the bench you dissolve a known mass of powder in a known volume of a suitable diluent, which gives you a solution of known concentration. From that point the peptide is handled as a liquid reagent, and the only number that matters for handling is the concentration, expressed in milligrams per millilitre (mg/mL).

Choosing a diluent

The two liquids most commonly used as laboratory reagents to reconstitute peptides are bacteriostatic water and sterile water. Both are chosen here purely as bench reagents.

• Bacteriostatic water is water containing a small amount of benzyl alcohol (typically around 0.9%) which suppresses microbial growth. Because it resists contamination, a reconstituted vial made up with it tends to remain usable as a laboratory stock for longer.
• Sterile water contains no preservative. It is appropriate where the benzyl alcohol would interfere with the work, or where a solution is to be used quickly and then discarded.

Some peptides are poorly soluble in plain water and their Certificate of Analysis or technical notes may indicate a different solvent for research handling. Always match the diluent to the chemistry of the specific compound rather than assuming one liquid suits everything.

The concentration maths

The whole calculation is a single relationship between mass, volume and concentration:

concentration (mg/mL) = mass in the vial (mg) ÷ volume of diluent added (mL)

You decide on a target concentration that is convenient to handle, then add the volume of diluent that produces it. Two neutral worked examples:

Mass in vial	Diluent added	Resulting concentration
10 mg	2 mL	5 mg/mL
10 mg	1 mL	10 mg/mL
5 mg	2.5 mL	2 mg/mL

To work out how much of the solution contains a given mass of peptide, rearrange the same relationship: volume (mL) = mass wanted (mg) ÷ concentration (mg/mL). For a 5 mg/mL solution, 0.1 mL contains 0.5 mg of peptide. That is arithmetic about the concentration of a laboratory stock, nothing more.

One refinement for precise work: the number on the label is the peptide plus its counterion and residual water, so the true peptide mass can be lower. Where exact quantity matters, use the net peptide content from the Certificate of Analysis rather than the nominal label mass. See our guide on salt forms and net peptide content.

Good aseptic technique

Reconstitution should be done cleanly so the stock solution is not contaminated or degraded.

• Work on a clean surface and wipe the vial stopper and the diluent stopper with an alcohol wipe before piercing.
• Draw up the chosen volume of diluent and add it slowly, letting it run down the inside wall of the vial rather than firing it directly onto the powder cake.
• Swirl gently, do not shake. Peptides are sensitive to mechanical stress and shaking introduces shear and foaming that can denature the molecule. A slow swirl, or simply leaving the vial to stand for a few minutes, lets the cake dissolve without stressing it.
• Let the solution settle and inspect it. It should be clear with no visible particulates. Cloudiness or persistent undissolved material is a quality signal worth investigating, not something to force into solution.

Storing the reconstituted vial

Once in solution the peptide is far less stable than the dry powder and its stability becomes cold-chain dependent. Keep the reconstituted vial refrigerated and protected from light, label it with the concentration and the date it was made up, and treat it as a short-lived working stock. For anything longer, the dry lyophilised material remains the stable form. Our storage and shelf life guide covers this in detail.

For research use only. Not for human consumption. Not a medicine, supplement or cosmetic. No therapeutic use is stated or implied.