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These tools calculate quantities for laboratory planning. They do not select a solvent, verify solubility or establish sample quality. For laboratory research only. Not for human or animal use.
From peptide mass to molar concentration
Molar concentration describes the amount of a substance in moles per volume of solution. A mass concentration, such as mg/mL, answers a different question: how much mass is present in that volume. Converting between them requires the molar mass of the chemical entity being counted.
Use c = m ÷ (M × V), where c is concentration in mol/L, m is mass in grams, M is molar mass in g/mol and V is final solution volume in liters. One mol/L is one molar, written 1 M. Millimolar, micromolar and nanomolar correspond to 10⁻³, 10⁻⁶ and 10⁻⁹ mol/L.
The first tool converts the entered mass and volume units before applying this equation. Its optional peptide-content field is a mass-fraction correction supplied by you; it is not an estimate obtained from the sequence or product name. Leave it at 100 when you want an uncorrected nominal calculation or when your entered mass is already net peptide mass.
Worked example: 2 mg in a final volume of 4 mL
Consider an illustrative peptide entity with a molar mass of 1,000 g/mol. If 2 mg of that entity is present in a final solution volume of 4 mL, the mass concentration is 0.5 mg/mL. Convert 2 mg to 0.002 g and 4 mL to 0.004 L before calculating the amount and concentration.
The amount is 0.002 g ÷ 1,000 g/mol = 0.000002 mol, or 2 µmol. Dividing by 0.004 L gives 0.0005 mol/L = 0.5 mM = 500 µM. The same arithmetic applies whether the input is entered as 2 mg and 4 mL or as 2,000 µg and 4,000 µL.
| Quantity | Equivalent values |
|---|---|
| Mass | 2 mg = 2,000 µg = 0.002 g |
| Final volume | 4 mL = 4,000 µL = 0.004 L |
| Amount | 2 µmol |
| Mass concentration | 0.5 mg/mL = 0.5 g/L |
| Molar concentration | 500 µM = 0.5 mM = 0.0005 M |
A shortcut for converting mg/mL to µM
When molar mass is expressed in g/mol, µM = mg/mL × 1,000,000 ÷ molar mass. For mM, use mg/mL × 1,000 ÷ molar mass. These shortcuts work because 1 mg/mL is numerically equal to 1 g/L; the remaining factors convert mol/L into the chosen molar unit.
For example, 0.25 mg/mL of a 2,000 g/mol peptide entity corresponds to 125 µM. Another peptide at the same 0.25 mg/mL can have a different molar concentration if its molar mass differs. The mass concentration alone cannot establish how many molecules are present.
Before comparing two experiments, check whether both concentrations use the same peptide entity and mass basis. A value derived from gross powder mass is not automatically comparable with a value corrected using a measured peptide-content fraction.
Gross mass, peptide content and purity
A weighed preparation may contain peptide, counterions, residual water and other components. If suitable documentation establishes a peptide mass fraction, multiply the gross mass by that fraction before converting the resulting peptide mass to moles. The molar mass must correspond to the entity represented by that corrected mass.
In the 2 mg example, an explicitly documented 80% peptide mass fraction would give 1.6 mg on the peptide basis and 400 µM in the same 4 mL final volume, using 1,000 g/mol. This is an arithmetic illustration, not an assay value for a NorthVerity product.
An HPLC area percentage is not automatically a mass fraction. Net peptide content and chromatographic purity describe different aspects of a material, and their use in a target-peptide concentration calculation depends on the analytical method and reporting basis. This tool does not multiply in an HPLC percentage or infer target-peptide purity.
Diluting a known stock: C₁V₁ = C₂V₂
For a dilution in which the amount of the solute is conserved, C₁V₁ = C₂V₂. C₁ is the stock concentration, V₁ the stock volume transferred, C₂ the target concentration and V₂ the final solution volume. Solving for the transfer gives V₁ = C₂V₂ ÷ C₁.
Suppose you need 10 mL at 100 µM from a 10 mM stock. First express the concentrations in the same units: 10 mM is 10,000 µM. The transfer volume is 100 × 10 ÷ 10,000 = 0.1 mL, or 100 µL. Transfer that volume and prepare the solution to a total final volume of 10 mL.
If volumes are treated as additive, the corresponding diluent estimate is 9.9 mL. The calculator displays both the transfer and the required final volume because final volume is the controlling quantity. The equation does not determine a compatible solvent or establish that the peptide remains dissolved.
| Input or result | Value |
|---|---|
| Stock concentration | 10 mM |
| Target concentration | 100 µM |
| Final solution volume | 10 mL |
| Stock volume to transfer | 100 µL |
| Diluent estimate if volumes are additive | 9,900 µL |
Checks before relying on the number
Use final solution volume rather than assuming that the volume of solvent added equals the completed solution volume. Keep unit conversions visible in the record. Mixing mg with µg, or mM with µM, changes the answer by a factor of one thousand.
A target concentration higher than the stock cannot be obtained by dilution alone. Equal stock and target concentrations require no dilution. If the computed transfer is below the validated working range of your equipment, the displayed number is not a practical pipetting instruction; plan an appropriate intermediate dilution under your laboratory method.
The arithmetic assumes the material represented by the entered mass is present in the solution on the specified basis. Incomplete dissolution, adsorption, precipitation, degradation and transfer losses are separate experimental questions. A calculated concentration is not an analytical measurement of the final solution.
Record the material identifier, lot, chemical form, mass basis, molar mass source, final volume, calculations and preparation date. For procurement questions, request the documents for the offered lot and resolve missing information before treating a nominal value as verified.
Frequently asked questions
Can I convert mg/mL to µM without a molecular weight? No. Molar concentration counts amount in moles, so the relevant molar mass is required. A mass concentration can still be reported without it.
Is 1 mg/mL equal to 1 µg/µL? Yes. Both the numerator and denominator change by a factor of 1,000, leaving the same mass concentration.
Does this calculator select a solvent or storage condition? No. Use material-specific documentation and a suitable laboratory method. The calculation supplies quantities, not evidence of solubility, stability or biological suitability.
Serial dilution: formula, table and worked examples
A serial dilution uses the solution from one dilution to prepare the next. In this worksheet, every step uses the same dilution factor and the same prepared volume. The original stock is the starting point, not tube 1. This makes the first diluted concentration C₀/D and the concentration at step n equal to C₀/Dⁿ.
Here D is a reduction factor greater than 1. A tenfold dilution means one part of the previous solution in ten total parts: one part sample plus nine parts diluent when volumes are additive. It does not mean one part sample plus ten parts diluent. Other references may use the word dilution for the remaining fraction, 1/D; record the convention with your numbers.
If V is the prepared volume in each tube, the transfer volume is V/D. The diluent estimate is V − V/D. Enter the initial concentration in M, mM, µM or nM; the table keeps that concentration unit throughout. All exported volumes are labeled in µL, even when the input uses mL or L.
The third calculator applies these equations for 1–48 steps. The volumes describe a planning model with additive volumes, a homogeneous mixture and no solute lost during transfer. A different method, variable step factors or additional sampling requires a separate plan.
Four tenfold steps from a 1,000 µM stock
Choose a 1,000 µM starting solution, a factor of 10, four dilution steps and a prepared volume of 1,000 µL per tube. Each step receives 100 µL from its stated source and an estimated 900 µL of compatible diluent. The successive concentrations are 100, 10, 1 and 0.1 µM.
Only the first 100 µL comes from the original stock. The second transfer comes from tube 1, the third from tube 2 and the fourth from tube 3. The total diluent estimate is 4 × 900 = 3,600 µL. These quantities exclude extra material for dead volume, losses or repeats.
After the onward transfer, tubes 1–3 each retain 900 µL. Tube 4 retains 1,000 µL because this plan includes no transfer out of the last tube. Removing a representative aliquot from a well-mixed tube reduces its volume but leaves its concentration unchanged. If you need at least 1,000 µL left in every tube, a prepared volume of 1,000 µL is insufficient for the earlier tubes.
| Step / source | Concentration (µM) | Transfer in | Diluent estimate | Left after onward transfer |
|---|---|---|---|---|
| 1 / stock | 100 | 100 | 900 | 900 |
| 2 / tube 1 | 10 | 100 | 900 | 900 |
| 3 / tube 2 | 1 | 100 | 900 | 900 |
| 4 / tube 3 | 0.1 | 100 | 900 | 1,000 |
Twofold series and planning the volume left over
For a 20 µM starting solution, a factor of 2 and 200 µL prepared per tube, each step combines 100 µL of the preceding solution with an estimated 100 µL of diluent. Four steps give 10, 5, 2.5 and 1.25 µM. The first three tubes retain 100 µL after onward transfer; the last retains 200 µL.
For this constant-volume model, the amount left in an earlier tube is R = V × (1 − 1/D). To retain at least R in those tubes, use V = R × D/(D − 1), then check vessel capacity and transfer range. For example, retaining 200 µL in each earlier tube of a twofold series requires 400 µL prepared per tube and a 200 µL transfer. The last tube would contain 400 µL unless your separate method specifies a withdrawal.
A twofold series and a tenfold series cover different concentration spacing. Choose the factor from the experimental method and required range. The calculator does not select an assay concentration, biological exposure or treatment dose.
Copy the dilution table and check the worksheet
Copy table produces a tab-separated worksheet for a spreadsheet. Download CSV includes the initial concentration, step factor, source tube, prepared volume, transfer, diluent estimate and volume remaining after onward transfer. If clipboard access is unavailable, the tool shows selectable text as a fallback. Input changes clear the old result so an exported table belongs to the displayed calculation.
Check the lowest concentration, transfer size, available stock and liquid remaining in every tube. A calculated transfer below 1 µL is flagged for review against the validated equipment range; a larger number is not automatically suitable for every pipette. Mix according to the laboratory method before taking the next aliquot, and consider transfer losses separately.
The CSV is a calculation record, not a measurement or a complete laboratory protocol. Keep material identity, lot, solvent, preparation date and any experimental adjustments in the accompanying record. Solubility, adsorption, stability and instrument performance are not inferred from the dilution factor.
Connect the calculation to material documentation
For peptide procurement, first establish what the starting concentration represents: the stated chemical form, the mass basis and the relevant molar mass. The molecular-weight calculator can help with a supported sequence, while the purity and net-content guide explains why an HPLC area percentage is not automatically a correction to weighed mass.
Review the available material information and ask for the documentation for the offered lot when requesting a written quote. Include the material identifier and the missing information you need to resolve. The calculation itself does not verify the supplied material, current availability or the offered lot.
Peptide Molecular Weight Calculator
Equations and documentation references
For laboratory research. Not for human or animal use.