This free online molarity calculator includes a protein molarity calculator for kDa-based concentration and amount conversions, plus single-solute calculations, multi-solute recipes, and stock-multiplier scaling for buffers, media, and stocks.
Useful Checks
Use this with the Dilution Calculator when a prepared stock solution needs to be diluted or converted to a final working concentration.
Multi-solute mode builds buffer, media, stock, stain, and assay recipes while keeping component units, molecular weights, 1x targets, and stock-multiplier amounts together.
Protein mode converts between protein mass concentration and molarity, or between protein mass and mole amount, using protein molecular weight in kDa.
For stock multipliers, enter the intended 1x working targets. If you choose 5x, 10x, 20x, or a custom multiplier, the result keeps the 1x amount visible beside the stock amount so manual multiplication errors are easier to catch.
Components can use molar units, % w/v, % v/v, mg/mL, µg/mL, or g/L, with molecular weight requested only where it is needed.
Selected liquid acids can use editable % w/w assay and density values, so the result reports stock volume plus the pure-acid equivalent.
Minimum Inputs Needed
For single solute: choose a calculation mode, then enter the values that mode requests. Molecular weight or a selected compound is required only for molar conversions.
Required mass modes use target concentration and final volume; reverse calculations may instead use weighed mass, g/L, or target molarity.
For % w/v mass: percent and final volume; molecular weight is not used.
For multi-solute: recipe volume and at least one component.
For protein mode: protein molecular weight in kDa and either concentration or amount.
Optional Settings
Calculator mode
Select Single solute for one compound, Multi-solute for a buffer or recipe, or Protein molarity for kDa-based protein conversions.
Calculation mode
In Single solute, choose required mass from target concentration, required mass from % w/v, molarity from weighed mass and volume, final volume from weighed mass and target molarity, molarity from g/L, or g/L from molarity.
Stock multiplier
Use this only when preparing a concentrated stock such as 5x, 10x, or 20x. At 1x, the tool shows only the working-solution amount. Above 1x, it shows both the 1x working amount and the stock amount.
Compound search (optional)
Search common compounds to fill molecular weight automatically.
Liquid acid stock
Appears for supported liquid acids. Edit the bottle assay in % w/w and density in g/mL before using the calculated stock volume.
Molecular weight
Needed for molar calculations if you do not select a compound.
Preferred mass unit
Choose the unit used to display the mass. Auto is usually suitable.
Protein calculation mode
Choose mass concentration to molarity, molarity to mass concentration, protein mass to mole amount, or mole amount to protein mass.
Component unit
For multi-solute recipes, choose the unit for each component: molar, % w/v, % v/v, mg/mL, µg/mL, or g/L.
How To Use: Single Solute
Select Single solute.
Select the calculation mode that names the result you need.
Enter the values requested for that direction, such as concentration, mass, molecular weight, or final volume.
Select a compound or enter molecular weight for molar calculations.
If liquid acid stock fields appear, check the % w/w assay and density against the bottle label or SDS.
Choose a stock multiplier only if making a concentrated stock.
Click Calculate.
How To Use: Multi-Solute Recipe
Select Multi-solute.
Enter the final recipe volume.
Choose 1x, 5x, 10x, or a custom stock multiplier.
Add each component and enter its 1x target.
Choose the unit for each component: molar, % w/v, % v/v, mg/mL, µg/mL, or g/L.
Enter molecular weight only for components using molar units, unless you select a compound from search.
For selected liquid acids, check the % w/w assay and density shown inside that component row.
Click Calculate.
How To Use: Protein Molarity
Select Protein molarity.
Enter the protein molecular weight in kDa.
Choose one of the four conversion directions: concentration-to-concentration or amount-to-amount.
Enter the concentration or amount and choose the input/output units.
Click Calculate.
Understanding The Results
The quick result shows the requested output: mass, molarity, final volume, g/L, protein concentration, protein mass, or mole amount.
For liquid acids, the quick result reports stock volume to add, and the detailed table keeps the pure-acid equivalent visible.
At 1x, the result shows only the amount for the final working solution.
For stock multipliers above 1x, the quick result and detailed table show both the 1x working amount and the selected stock amount.
In multi-solute stock mode, each row keeps the 1x target beside the stock target and amount to add.
The final step tells you to bring the complete mixture to the final recipe volume, not to add that much water on top.
Warnings may appear for very small masses, high concentrations, high % v/v totals, or solubility concerns.
Protein mode shows the converted value, selected conversion direction, output unit, and protein molecular weight used.
Protein mode accepts kDa for molecular weight, common mass concentration units, molar concentration units, mass amount units, and mole amount units.
Assumptions And Limitations
Compound values are reference values from a curated offline list. Verify the exact reagent form you use.
Liquid acid defaults are starter values for common concentrated acids; supplier assay, density, temperature, and dilution can vary.
Solubility warnings are approximate.
% w/v means grams per 100 mL final solution.
% v/v is a volume-to-add calculation, not a mass calculation.
For multi-solute stock recipes, component targets are treated as 1x working targets and multiplied for the stock recipe.
Protein mode assumes the entered kDa value is the protein form you care about. Tags, cleavage, glycosylation, multimers, or processing can change the relevant molecular weight.
Protein molarity is an amount-concentration conversion; it does not predict activity, oligomerization state, purity, or functional protein concentration.
Examples
Single solute: To make 100 mL of 10 mM Tris, search Tris or enter the molecular weight, set 10 mM and 100 mL, then calculate the mass.
Liquid acid: To make 100 mL of 100 mM HCl, select hydrochloric acid, check the 37% w/w assay and 1.19 g/mL density, then use the calculated concentrated-acid volume.
Multi-solute: To make a 5x buffer stock, enter the final stock volume, choose 5x, add each component at its 1x target, then prepare the listed 5x amounts and bring the mixture to the final volume.
Protein: For a 50 kDa protein at 1 mg/mL, choose mass concentration to molarity. The result is 20 µM.
Use note: These tools are for research and educational planning. Check important calculations and sequence designs before ordering reagents or running experiments.