Peptide Molarity Calculator
Calculate solution molarity in mM and µM from peptide mass, molecular weight and volume.
Calculate Peptide Molarity
Enter the peptide mass, its molecular weight, and the solution volume. Molarity is returned in millimolar (mM) and micromolar (µM).
Molecular weight must come from reliable compound documentation, such as the certificate of analysis or supplier specification sheet. This calculator does not look up or estimate it.
Results update instantly as you type. This tool performs a mathematical calculation only — always independently verify results before using them in a laboratory procedure.
How This Calculator Works
Molarity expresses the number of moles of peptide per litre of solution. Because moles cannot be measured directly, molarity is calculated from a mass, a molecular weight, and a volume. The molecular weight is specific to each peptide and must be supplied by the user from reliable documentation — this calculator has no compound database and does not estimate it.
Formula and Unit Definitions
Molarity (mol/L) = peptide mass (mg) ÷ [molecular weight (g/mol) × volume (mL)]
Molecular weight is expressed in grams per mole (g/mol), numerically equivalent to Daltons (Da) for a peptide. mM (millimolar) is one-thousandth of a mole per litre; µM (micromolar) is one-millionth of a mole per litre. The calculator computes molarity in mol/L internally, then converts to mM and µM for display.
Worked Laboratory Example
Suppose you have 5 mg of a peptide with a molecular weight of 1,000 g/mol, dissolved in 2 mL of solvent.
Molarity = 5 mg ÷ (1,000 g/mol × 2 mL) = 0.0025 mol/L
= 2.5 mM (2,500 µM)
Accuracy and Limitations
- The molecular weight must be entered correctly from reliable compound documentation — an incorrect value produces an incorrect molarity, and this calculator cannot detect the error.
- Results are only as accurate as the mass, molecular weight and volume values supplied.
- This calculator does not account for peptide purity, salt content, or counter-ion mass, all of which can affect true molarity.
See the full calculation methodology for rounding rules and validation logic.
Frequently Asked Questions
Where do I find a peptide’s molecular weight?
The molecular weight must come from reliable compound documentation, such as the certificate of analysis or supplier specification sheet. This calculator does not look up, estimate or store molecular weight values.
Is molecular weight the same as Daltons?
For peptides, the numeric value of molecular weight in grams per mole (g/mol) is the same as the value in Daltons (Da). Enter the number from your documentation into the molecular weight field regardless of which unit label it uses.
Why is molarity shown in mM and µM instead of mol/L?
Peptide solutions are typically prepared at concentrations that are extremely small in mol/L, so millimolar (mM) and micromolar (µM) are the units most commonly used and referenced in laboratory protocols.
Can this calculator be used for human or animal dosing?
No. This calculator is not designed for, and must not be used for, human or animal dosing. It is a mathematical tool intended for laboratory research only.