Molarity Calculator
Solve for molarity, mass of solute, or solution volume from any two known quantities. Choose mass units (g, mg, ug), volume units (L, mL, uL), and concentration units (M, mM, uM, nM). A reference table of common chemicals and full unit conversions are shown with every result.
Formula
Worked example
58.44 g NaCl (molar mass 58.44 g/mol) in 1 L gives 1.000 mol and 1.000 M. To prepare 500 mL of 10 mM glucose: mass = 0.010 mol/L x 0.500 L x 180.16 g/mol = 0.901 g.
Three modes: solve for molarity, mass, or volume
Classic molarity calculators only compute M from mass and volume. This calculator works in three directions. Set "Solve for" to "Molarity (concentration)" and enter the mass of solute and the final solution volume to get the molar concentration. Set it to "Mass of solute" and enter the target concentration and the volume you want to prepare, and the calculator tells you exactly how much solid to weigh out: mass = M x V x molar mass. Set it to "Solution volume" and enter the mass you have and the target concentration, and the calculator returns the volume of solution you can prepare: V = n / M. All three modes share the same underlying relationship: M = n / V = (mass / molar mass) / volume.
Units: grams, milligrams, microlitres, mM, uM, nM
Biochemistry and pharmacology routinely work at concentrations far below 1 M and with sub-milligram quantities. This calculator accepts mass in grams, milligrams, or micrograms, and volume in litres, millilitres, or microlitres. Target concentration can be entered in M, mM, uM, or nM. All values are converted to SI base units internally before any arithmetic, so mixing units introduces no rounding error. The output panel always shows the full concentration set: mol/L, mM, uM, g/L, and mg/mL.
How to find the molar mass
The molar mass is the sum of the atomic masses of every atom in the molecular formula, in grams per mole, equal numerically to the molecular weight. For common reagents it is printed on the bottle label as "FW" (formula weight) or "MW" (molecular weight). For compounds you look up, use the IUPAC-recommended atomic weights published by NIST. Examples: NaCl = 22.99 + 35.45 = 58.44 g/mol; glucose (C6H12O6) = 6 x 12.01 + 12 x 1.008 + 6 x 16.00 = 180.16 g/mol; NaOH = 22.99 + 16.00 + 1.008 = 40.00 g/mol. The reference table above lists molar masses for 14 common lab reagents.
Volume of solution versus volume of solvent
A common preparation error is entering the volume of water added rather than the total volume of the finished solution. The correct procedure is to add the solid to a volumetric flask, dissolve it in most of the solvent, then top up to the final calibration mark. The volume change on dissolution, usually small for dilute solutions, means the final volume can differ slightly from the water volume added. For example, dissolving 58.44 g NaCl in exactly 1 L of water gives slightly less than 1 L of solution, because the salt partially fills the liquid volume.
Temperature, solubility, and hydrated salts
Molarity is temperature-dependent: most solutions expand when heated, increasing volume and diluting the concentration. Reference concentrations are usually stated at 20 degrees C or 25 degrees C. The calculator assumes complete dissolution. If the target concentration exceeds the compound's solubility limit, the actual molarity will be lower than calculated. For hydrated salts, always enter the molar mass of the hydrated form. For example, copper sulfate pentahydrate (CuSO4-5H2O) has MW = 249.69 g/mol, not 159.60 g/mol for the anhydrous form. Using the anhydrous MW gives a lower actual concentration than intended.
Molarity vs. molality vs. normality
Molarity (M or c) is moles of solute per litre of solution and is the standard unit in volumetric analysis and most bench chemistry. Molality (m) is moles of solute per kilogram of solvent, which is temperature-independent and preferred for colligative-property calculations (boiling-point elevation, freezing-point depression). Normality (N) is equivalents of reactive species per litre, used in acid-base and redox titrimetry where one equivalent can differ from one mole. For everyday bench preparation, molarity is the universal standard.
Common chemicals: molar mass and typical working concentrations
| Compound | Formula | Molar mass (g/mol) | Typical working concentration |
|---|---|---|---|
| Sodium chloride | NaCl | 58.44 | Physiological saline: 0.154 M (0.9% w/v) |
| Glucose | C6H12O6 | 180.16 | Cell culture: 5-25 mM |
| Sodium hydroxide | NaOH | 40 | Lab base: 0.1-1 M |
| Hydrochloric acid | HCl | 36.46 | Concentrated ~12 M; working 0.1-1 M |
| Sulfuric acid | H2SO4 | 98.08 | Concentrated ~18 M; working 1 M |
| Sodium bicarbonate | NaHCO3 | 84.01 | Buffer: 25-100 mM |
| Tris base | C4H11NO3 | 121.14 | Buffer: 10-100 mM (pH 7.4-8.0) |
| EDTA (disodium salt) | C10H14N2Na2O8 | 336.21 | Chelation: 0.5-10 mM |
| Potassium chloride | KCl | 74.55 | Electrolyte: 5-150 mM |
| Ammonium sulfate | (NH4)2SO4 | 132.14 | Protein precipitation: 0.1-2 M |
| Acetic acid | CH3COOH | 60.05 | Glacial ~17.4 M; acetate buffer 0.1-1 M |
| Phosphoric acid | H3PO4 | 98 | Buffer: 10-200 mM |
| CuSO4 pentahydrate | CuSO4-5H2O | 249.69 | Solutions: 10-100 mM (use hydrated MW) |
| Sucrose | C12H22O11 | 342.3 | Osmotic agent: 0.25-1 M |
Reference values for frequently prepared lab solutions. Molar masses from IUPAC 2021 atomic weights. Enter the molar mass directly to use any compound.
Frequently asked questions
How do I calculate molarity from mass and volume?
Divide the mass of solute in grams by its molar mass in g/mol to get moles, then divide moles by the total solution volume in litres: M = (mass / molar mass) / volume. For example, 5.85 g NaCl (molar mass 58.44 g/mol) in 500 mL = 0.100 mol / 0.500 L = 0.200 M.
How do I solve for mass instead of molarity?
Set "Solve for" to "Mass of solute". Enter the molar mass, the target concentration, and the volume. The calculator returns the grams to weigh out using mass = M x V x molar mass. For example, to make 250 mL of 50 mM NaCl: 0.050 x 0.250 x 58.44 = 0.731 g.
What is the difference between molarity and molality?
Molarity (M) is moles of solute per litre of solution, so it changes with temperature as solution volume expands or contracts. Molality (m) is moles of solute per kilogram of solvent, making it temperature-independent. For most room-temperature lab preparations, molarity is the standard unit.
How do I find the molar mass of a compound?
Add the atomic masses of every atom in the molecular formula using IUPAC values from a periodic table. For example, NaCl = 22.99 + 35.45 = 58.44 g/mol. The value is also printed on reagent bottles as FW or MW. Use the reference table above for 14 common lab chemicals.
Can I use this calculator for dilution problems?
This calculator prepares solutions from a solid solute. For diluting a concentrated stock, use the dilution equation C1V1 = C2V2 separately, using the molarity from this tool as your starting concentration C1.
How do I handle hydrated salts?
Enter the molar mass of the hydrated form, not the anhydrous form. Copper sulfate pentahydrate (CuSO4-5H2O) has MW = 249.69 g/mol, not 159.60 g/mol. Using the anhydrous MW will give you a lower actual concentration than intended, because the water of crystallisation adds to the weighed mass.
Why does molarity change with temperature?
Most solutions expand when heated, increasing volume and decreasing moles per litre. Reference concentrations are defined at a fixed temperature, typically 20 degrees C or 25 degrees C. For precise work, prepare and measure solutions at controlled temperature and use a thermostated volumetric flask.