Peptide calculator
Work out the concentration of a peptide stock solution from the powder in the vial and the liquid you add, how much liquid gives the concentration you want, or how much stock holds a set amount.
How it's worked out: concentration = peptide mass × net content ÷ liquid volume
How to work out a peptide's concentration
A vial of freeze-dried peptide holds a set mass of powder. Adding a known volume of liquid turns it into a stock solution, and its concentration is simply mass ÷ volume. A 5 mg vial with 2 mL added comes to 5 ÷ 2 = 2.5 mg/mL, which is the same as 2.5 µg/µL. Less liquid makes a stronger stock and more liquid a weaker one.
To hit a concentration you've chosen, turn it round: volume = mass ÷ concentration. For 1 mg/mL from a 5 mg vial, add 5 mL, as long as the vial holds that much. If it doesn't, make a stronger stock and dilute it later with the dilution calculator.
Peptide concentration chart
The stock concentration in mg/mL for common fills (rows) and volumes of liquid added (columns). mg/mL and µg/µL (mcg/µL) are the same number.
| Fill | 1 mL | 2 mL | 3 mL | 5 mL |
|---|---|---|---|---|
| 1 mg | 1 | 0.5 | 0.333 | 0.2 |
| 2 mg | 2 | 1 | 0.667 | 0.4 |
| 5 mg | 5 | 2.5 | 1.67 | 1 |
| 10 mg | 10 | 5 | 3.33 | 2 |
5 mL won't fit a standard 3 mL vial. For a weaker solution, make the stock in the vial and dilute some of it in a larger tube. The chart counts the whole fill; enter a net peptide content in the calculator to correct for it.
Taking a set amount from the stock
To add a known amount of peptide to an assay, a standard curve or a reaction, divide the amount by the stock's concentration: volume = amount ÷ concentration. From a 2 mg/mL stock, 250 µg (mcg) is 250 ÷ 2,000 = 0.125 mL, or 125 µL. Enter a molar mass to work in nmol instead. For volumes under about 10 µL, dilute the stock first so the pipetting stays accurate.
Why net peptide content changes the answer
The mass on the label is the whole fill: peptide plus counter-ions (often acetate or trifluoroacetate) and a little water. The peptide itself is usually 70 to 90% of it. If the COA gives a net peptide content, enter it and the calculator works from the peptide alone. A 5 mg fill at 80% holds 4 mg of peptide, so 2 mL gives 2 mg/mL, not 2.5. The guide to net peptide content explains how it differs from purity.
From mg/mL to molarity
Assays are often set up in molar units. Divide the mass concentration by the molar mass: mM = mg/mL ÷ molar mass (g/mol) × 1,000. A peptide of 1,419.5 g/mol at 2 mg/mL is about 1.41 mM. Each product's molar mass is in its Technical data, and the molarity calculator converts in both directions.
Splitting a stock into aliquots
A peptide in solution breaks down far faster than the dry powder, and each freeze and thaw adds to it. Splitting the stock into equal tubes means each one thaws once. Enter an aliquot size to see how many tubes a stock fills. For the bench steps, from warming the vial to keeping the solution cold, see how to reconstitute peptides and how to store peptides.
What this calculator is for
It does solution maths for laboratory work: concentrations, volumes, molarity and aliquots, in mg, µg, nmol, mL and µL. Our products are for research use only and are not for human or veterinary use.