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Peptide calculator

Stock concentration, aliquot transfer volume and dilution for lyophilised research peptides — in-vitro laboratory use only.

For research use only. Not for human or veterinary use. Sold strictly for in-vitro laboratory research; not for diagnosis or treatment.

Stock concentration

The concentration of a stock solution made from the whole vial.

Stock concentration
5 mg/mL5 µg/µL

Aliquot transfer volume

The volume of stock solution that holds one aliquot.

Taken from the stock concentration above.

Transfer volume
0.2 mL200 µL

Dilution (C1V1 = C2V2)

Choose the unknown term and enter the other three.

Stock volume (V1)
0.2 mL200 µL
Solvent to add
0.8 mL800 µL

How the calculator works

The calculator runs three pieces of stock-solution arithmetic, and every figure updates as you type.

  • Stock concentration: the peptide mass in the vial (mg) divided by the solvent volume added (mL), giving mg/mL.
  • Aliquot transfer volume: the aliquot mass divided by the stock concentration, giving the volume of stock to pipette in mL and µL.
  • Dilution: C1 × V1 = C2 × V2. Enter any three of stock concentration (C1), stock volume (V1), final concentration (C2) and final volume (V2), and the calculator solves for the fourth and the solvent to add.

Figures are shown to four significant figures. A transfer volume under 10 µL is flagged, because volumes that small are difficult to pipette accurately.

Units and conversions

The calculator converts units for you. The relationships are:

  • 1 mg = 1000 µg, and 1 g = 1000 mg.
  • 1 mL = 1000 µL, and 1 L = 1000 mL.
  • 1 mg/mL = 1000 µg/mL = 1 µg/µL.

Because 1 mg/mL equals 1 µg/µL, a stock concentration in mg/mL also tells you how many micrograms each microlitre holds.

Worked examples

Each example assumes the whole vial is dissolved in the stated solvent volume.

  1. A 5 mg vial in 1 mL of solvent: 5 ÷ 1 = 5 mg/mL. A 1 mg aliquot is 1 ÷ 5 = 0.2 mL, or 200 µL.
  2. A 10 mg vial in 2 mL of solvent: 10 ÷ 2 = 5 mg/mL. A 0.5 mg aliquot is 0.5 ÷ 5 = 0.1 mL, or 100 µL.
  3. A 20 mg vial in 5 mL of solvent: 20 ÷ 5 = 4 mg/mL. A 2 mg aliquot is 2 ÷ 4 = 0.5 mL, or 500 µL.
  4. Dilution: to take a 5 mg/mL stock to 1 mg/mL in a final volume of 1 mL, V1 = 1 × 1 ÷ 5 = 0.2 mL of stock, made up with 0.8 mL of solvent.

Choosing solvent volume

The solvent volume sets the stock concentration, and the stock concentration sets how much you pipette for each aliquot. A 20 mg vial in 1 mL gives 20 mg/mL, so a 0.5 mg aliquot is only 25 µL. The same vial in 4 mL gives 5 mg/mL, and the same aliquot becomes 100 µL, a volume most laboratory pipettes handle comfortably.

Work backwards from the smallest aliquot you need: choose a solvent volume that keeps its transfer volume at 10 µL or more, and check that the total fits the vial.

Which solvent to use, and how the solution is handled and kept, are decisions for the receiving laboratory under its own procedures. The calculator makes no assumption about either.

Frequently asked questions

Divide the peptide mass in the vial by the volume of solvent added. 10 mg in 2 mL gives 10 ÷ 2 = 5 mg/mL, which is the same as 5 µg/µL.

Divide the aliquot mass by the stock concentration, keeping the units consistent. A 1 mg aliquot from a 5 mg/mL stock is 1 ÷ 5 = 0.2 mL, or 200 µL. To work in micrograms, divide the mass by 1000 first to convert it to milligrams.

Diluting a solution leaves the amount of solute unchanged; only the volume grows. C1 and V1 are the stock concentration and the volume of stock taken; C2 and V2 are the final concentration and final volume. Rearranged, V1 = C2 × V2 ÷ C1.

Very small volumes carry a larger relative pipetting error. If a transfer volume falls below 10 µL, a larger solvent volume gives a more dilute stock and a larger volume to pipette for the same aliquot mass.

No. Adding solvent can only lower a concentration, so the calculator expects a final concentration at or below the stock concentration, and a stock volume no larger than the final volume.

No. It takes the stated vial mass as the mass of peptide. If your laboratory corrects for net peptide content or counter-ions, apply that correction to the mass before entering it.