Arithmetic only: mass divided by volume. It does not account for the small volume of the powder itself, which is negligible at these quantities.
How the calculation works
Concentration is the mass of peptide divided by the volume of liquid it is dissolved in. A 10mg vial reconstituted with 2ml of water gives 10 ÷ 2 = 5mg per ml. Each 0.1ml of that solution holds 0.5mg, which is 500 micrograms.
The only choice is the volume of water. More water gives a weaker solution that is easier to measure in small amounts. Less water gives a stronger one.
Common combinations
Two worked examples
- 01Finding the water for a target concentrationA 10mg vial is wanted at 2mg per ml. Divide the mass by the target: 10 ÷ 2 = 5, so 5ml of water gives 2mg per ml.
- 02Finding the mass in a measured volumeA solution is 3.33mg per ml and 0.3ml is drawn. Multiply the two: 3.33 × 0.3 = 1mg, to the nearest hundredth.
Both are the same relationship rearranged. Concentration equals mass divided by volume, so volume equals mass divided by concentration, and mass equals concentration multiplied by volume.
Milligrams and micrograms
Labels use milligrams (mg). Protocols often use micrograms (mcg). There are 1,000 micrograms in a milligram, so 0.25mg is 250mcg. Mixing the two up is the most common arithmetic error in peptide work, and it is a thousand-fold one.
Other common mistakes
- Reading the mass on the label as a concentration. A 10mg vial is 10mg in total, whatever volume it ends up in.
- Forgetting liquid already in the vial. Adding water to a solution dilutes it, and the calculation has to use the new total volume.
- Rounding too early. 10 ÷ 3 is 3.33 recurring, and carrying 3.3 through several steps drifts.
Pre-mixed vials need no calculation
Everything in our range ships already in solution, so the concentration is fixed by the label. It is the content divided by the 3ml fill.
Using it as a peptide pen calculator
A pen is a pre-mixed product, so the same arithmetic applies with the numbers printed on it. Enter the mass of peptide the pen holds and the volume of solution in the cartridge, and the result is the concentration in mg per ml.
A blend pen holds more than one peptide in the same solution. Work each one out separately against the same volume. A pen holding 50mg of one peptide and 10mg of another has five times the concentration of the first as of the second, whatever the volume.
One calculation, several names
Reconstitution calculator, peptide mixing calculator and peptide concentration calculator all describe this same sum: mass divided by volume. Tools that go further and suggest an amount to use are doing something different, and this one does not.
For the method itself, see reconstituting a lyophilised vial, and what bacteriostatic water is for the water to use.