Peptide Molarity Calculator
Research Tools / Concentration
Use this calculator to convert a peptide's mass concentration to molar concentration, convert molarity back to mass concentration, or find molarity from a weighed mass and final volume. Enter a positive molecular weight in g/mol, and the calculator returns results in mg/mL, mM and µM. Mass and volume mode can also show the total amount in µmol. Calculations run in your browser with no account required.
For laboratory research calculations.
Convert peptide concentration
Your result
Enter your values and choose Calculate.
Total amount µmol
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How to convert mg/mL and molarity
Choose the mode that matches what you already know. Mass concentration to molarity accepts mg/mL, µg/mL or g/L. Molarity to mass concentration accepts M, mM, µM or nM. Mass and final volume to molarity accepts mg, µg or g with a final volume in mL, µL or L.
Every mode rests on one relationship. Because 1 mg/mL equals 1 g/L, molarity in M equals mg/mL divided by molecular weight in g/mol. Multiply M by 1,000 for mM or by 1,000,000 for µM. In mass and volume mode, the calculator first divides mg by final volume in mL to get mg/mL, then applies the same step. Enter the final solution volume.
| Start with | To find | Calculation |
|---|---|---|
| mg/mL | mM | mg/mL × 1,000 ÷ MW |
| mg/mL | µM | mg/mL × 1,000,000 ÷ MW |
| µg/mL | µM | µg/mL × 1,000 ÷ MW |
| µM | mg/mL | µM × MW ÷ 1,000,000 |
| mg and mL | mg/mL | mass in mg ÷ final volume in mL |
| mg | µmol total | mass in mg × 1,000 ÷ MW |
Worked examples
Use these examples to check the calculation in each mode.
1 mg/mL at 1,000 g/mol
1 mg/mL divided by 1,000 g/mol gives 0.001 M, which is 1 mM or 1,000 µM. This is a hypothetical compound used for illustration only.
50 µM at 2,000 g/mol
Multiply 50 µM by 2,000 g/mol and divide by 1,000,000 to get 0.1 mg/mL.
5 mg in 2 mL final volume at 2,500 g/mol
5 mg in 2 mL gives 2.5 mg/mL. Dividing by 2,500 g/mol gives 0.001 M, which is 1 mM or 1,000 µM. The total amount is 5 mg divided by 2,500 g/mol, which is 2 µmol.
Peptide molarity FAQs
How do I convert mg/mL to µM?
Divide mg/mL by molecular weight in g/mol, then multiply by 1,000,000. At 1,000 g/mol, 1 mg/mL is 1,000 µM. If you start in µg/mL, multiply by 1,000 and divide by MW to get µM directly.
How do I convert µM to mg/mL?
Multiply µM by molecular weight in g/mol and divide by 1,000,000. For mM, multiply by MW and divide by 1,000. At 2,000 g/mol, 50 µM is 0.1 mg/mL.
What do I need if I start from a labelled mass?
You need the mass, the final solution volume and a molecular weight on the same basis as that mass. Enter them in mass and final volume mode to get mg/mL, mM, µM and total µmol. Check what the stated mass represents, because a gross amount and a net peptide amount give different molarities.
How does µM differ from µg/mL?
µg/mL is a mass concentration, the mass of material per volume. µM is an amount concentration, micromoles of substance per litre. Converting between them requires the molecular weight. Total µmol is different again, because it is an amount of substance with no volume attached.
Where do I find a matching molecular weight?
Use the average molar mass for the exact material form you weighed, taken from analytical documentation or another traceable source. Our COA Finder may help you locate a certificate of analysis. Do not infer MW from an m/z value, and do not assume every report lists a form-specific value.
Why does salt form or modification matter?
Counterions and terminal modifications change molecular weight. If your mass includes a salt but your MW describes the free peptide, or the reverse, the molarity will be off by the ratio of the two weights. Match the MW to the form and basis of the entered mass.
Does HPLC purity give net peptide mass?
No. An HPLC purity percentage is not interchangeable with peptide mass fraction, and purity and content are separate values. The calculator adjusts for neither. If you need a corrected result, enter an independently established mass that fits the molecular form.
How do I find component molarity in a blend?
Each component has its own amount concentration. Run the calculation once per component, using that component's individual mass and its own molar mass. A combined mass or an averaged MW will not give valid component molarities. For blend-level work, see the Blend Calculator.
How is molarity conversion different from stock dilution?
This calculator converts between mass and amount concentration for one solution. Taking a known stock to a working concentration is a separate task covered by the Serial Dilution Calculator. To find concentration from one mass and final volume, you can also use the Reconstitution Calculator.
How should I read very small or rounded results?
Small values are often clearer in a smaller unit, so 0.0005 mM reads as 0.5 µM. Remember that 1 mM equals 1,000 µM and 1 µM equals 1,000 nM. Displayed values may be rounded, so keep full input precision for downstream work and record the unit with every result.
Continue with your lab task
Peptide Reconstitution Calculator
Start with the mass and final volume to find mass concentration.
Peptide Blend Calculator
Find the mass concentration of each blend component.
Serial Dilution Calculator
Plan a dilution from a stock of known concentration.
Peptide COA Finder
Find available documentation by product or lot.
Browse the research catalogue for listed product forms and options.
