Peptide Molarity Calculator
Enter a mass, a molecular weight, and a solvent volume to get the resulting molar concentration, expressed at whichever scale is most convenient — molar, millimolar, micromolar, or nanomolar.
Results
- Molarity
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- Molarity
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- Molarity
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- Molarity
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How this calculator works
Moles = mass ÷ molecular weight. Molarity = moles ÷ volume, with all inputs converted to grams and liters before dividing so any combination of mass and volume units gives a consistent result.
How to calculate peptide molarity
- Determine the mass of peptide you have, in any mass unit.
- Find (or calculate) the peptide's molecular weight, in g/mol.
- Divide mass by molecular weight to get moles.
- Divide moles by the solvent volume, in liters, to get molarity in mol/L.
Worked example: 1 mg of a peptide with a molecular weight of 1,000 g/mol, dissolved in 1 mL of solvent. 1 mg = 0.001 g, so moles = 0.001 ÷ 1,000 = 1 × 10⁻⁶ mol. 1 mL = 0.001 L, so molarity = 1 × 10⁻⁶ ÷ 0.001 = 1 × 10⁻³ mol/L, or 1 mM.
Frequently asked questions
Is this a peptide molar concentration calculator?
Yes — molarity and molar concentration are the same thing: moles of peptide per liter of solvent. Enter your mass, molecular weight, and volume above to get the result in M, mM, µM, or nM.
What is peptide molarity?
Molarity is concentration expressed as moles of peptide per liter of solvent (mol/L), rather than mass per volume (like mg/mL). Because it's mole-based, it accounts for the peptide's molecular weight — equal mg/mL concentrations of two different peptides give two different molarities.
How do I calculate peptide molarity?
Divide the peptide's mass by its molecular weight to get moles, then divide moles by the solvent volume in liters to get molarity in mol/L. Multiply by 1,000, 1,000,000, or 1,000,000,000 to express the result in mM, µM, or nM.
How do I convert mg/mL to molarity?
mg/mL and g/L are numerically identical, so you can divide a mg/mL concentration directly by the molecular weight in g/mol to get molarity in mol/L — no extra unit conversion needed.
Where do I get my peptide's molecular weight?
If you know the sequence but not the molecular weight, use the peptide molecular weight calculator first, then bring that number here.
Why does the same mg/mL concentration give different peptides different molarities?
Molarity is moles per liter, and moles depend on molecular weight. A heavier peptide has fewer moles in the same mass, so at equal mg/mL, the heavier peptide has the lower molarity.
Is this the same as the reconstitution calculator?
No. This is a research tool for molar concentration (mol/L), used in lab contexts like assay setup. The peptide reconstitution calculator instead converts a vial's mass and water volume into a mass concentration (mg/mL) and a syringe draw for a specific dose.
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Educational tool only, not medical advice — verify with a licensed clinician. See the full medical disclaimer.