Peptide calculator
Two calculators for preparing research peptide solutions: reconstitution, which gives the concentration of a vial once solvent is added and the volume that holds a given amount, and molarity, which converts mass and molecular weight to molar concentration. Molecular weights for every compound in our catalogue are built in.
For in-vitro laboratory preparation only. Nothing on this site is guidance for human or veterinary use.
Reconstitution calculator
A lyophilised vial contains a stated mass of peptide. Adding a known volume of solvent gives a solution of known concentration, and the volume that holds any amount of peptide follows directly: concentration is mass divided by volume, and the volume for a target amount is that amount divided by the concentration.
Worked example. 10 mg of peptide in 2 mL of solvent is 5 mg/mL, which is the same as 5 µg/µL. An aliquot holding 250 µg is therefore 50 µL.
If the batch certificate reports net peptide content, multiply the vial mass by that fraction before entering it, because lyophilised peptides carry bound water and counter-ions. Our guide to reading a certificate of analysis shows where that figure appears.
- Concentration
- 5 mg/mL
- Equivalent
- 5,000 µg/mL · 5 µg/µL
- Aliquot volume for 100 µg
- 20 µL (0.02 mL)
Concentration assumes the whole stated mass is peptide. Where the certificate reports net peptide content, multiply the vial mass by that fraction first.
Molarity calculator
In-vitro work is usually specified in molar terms, so a mass of peptide has to be converted using its molecular weight. Moles are mass in grams divided by molecular weight in g/mol; molarity is moles divided by volume in litres. The calculator also runs in reverse, giving the mass needed for a target molarity in a given volume.
Worked example. 10 mg of a peptide of 4,813 g/mol is 2.08 µmol. In 1 mL that is 2.08 mM, or 2,080 µM.
Choose a compound to fill in its molecular weight from our product specifications, or enter any value. For metal complexes such as GHK-Cu, use the mass of the complex where the certificate confirms it.
- Molar concentration
- 2.078 mM · 2,077.5 µM
- Moles of peptide
- 2.078 µmol
- Mass for 1 mM in 1 mL
- 4.813 mg
Use the average molecular weight from the product specification, or the net-peptide-corrected mass from the certificate.
Units and conventions
| Quantity | Unit | Note |
|---|---|---|
| Mass | mg, µg | 1 mg = 1,000 µg. Vial labels state nominal mass; the certificate states net content. |
| Volume | mL, µL | 1 mL = 1,000 µL. The final solution volume is taken as the solvent volume added. |
| Mass concentration | mg/mL, µg/µL, µg/mL | mg/mL and µg/µL are the same number. 1 mg/mL = 1,000 µg/mL. |
| Molar concentration | M, mM, µM | 1 mM = 1,000 µM. Most in-vitro literature reports µM or nM. |
| Molecular weight | g/mol (Da) | Average mass of the free peptide unless stated otherwise on the certificate. |
Solvent choice affects solubility and stability rather than the arithmetic; see choosing a reconstitution solvent and storage and stability. Solutions should be made fresh where possible and kept refrigerated; freeze-thaw behaviour varies by compound and is noted in each monograph.
Questions about the calculator
What does a peptide reconstitution calculator work out?
The concentration of the solution you get when a known mass of lyophilised peptide is dissolved in a known volume of solvent, and from that, the volume of solution that contains any given amount of peptide. Concentration in mg/mL is numerically the same as µg/µL.
Which solvent volume should I enter?
The volume you actually add to the vial. Lyophilised peptide occupies very little volume, so for research purposes the final volume is taken as the solvent volume; the error is well under one percent at the concentrations used in vitro.
Why does the certificate's net peptide content matter?
A lyophilised vial labelled 10 mg contains 10 mg of material, of which a fraction is bound water and counter-ion (usually trifluoroacetate or acetate). Where the certificate reports net peptide content, say 85%, the vial holds 8.5 mg of peptide. Enter that figure for an accurate concentration.
How is molarity calculated for a peptide?
Molar concentration is moles per litre. Moles are mass in grams divided by molecular weight in g/mol, so a 10 mg vial of a 4,813 g/mol peptide holds 2.08 µmol, which in 1 mL gives 2.08 mM. The calculator uses the molecular weight from our product specifications, or any value you enter.
Which molecular weight should I use?
The average molecular weight of the peptide as supplied, which for most research peptides is the free peptide (the counter-ion is excluded by the net-content correction). For metal complexes such as GHK-Cu, use the mass of the complex if the certificate confirms it was supplied as the complex.
Is this calculator for human or veterinary use?
No. It is a laboratory tool for preparing in-vitro solutions. Nothing on this site is guidance for use in people or animals, and everything we supply is for research use only.