Molarity Calculator
Calculate Mass, Volume, or Molarity
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How to Use This Molarity Calculator
Lab prep day means weighing out solute, grabbing a volumetric flask, and hoping you remembered the molarity formula correctly. This calculator solves for mass, volume, or molarity when you know the other two plus the compound's formula weight.
- Select Calculate. Choose Mass (g), Volume (V), or Molarity (M). The unknown field hides.
- Enter Formula Weight (MW). Type molecular weight in g/mol from your reagent label or the Molecular Weight Calculator.
- Fill Mass, Volume, and Molarity. Enter the two visible values with units—mass in g/mg/kg, volume in L/mL, molarity in M/mM.
- Press Calculate. Review the Result in convenient lab units.
For mass-from-density problems, pair with the Density Calculator. For stoichiometry beyond concentration, use your textbook mole ratios alongside these numbers.
Molarity Calculator Formulas and Practical Applications
Molarity connects moles of solute to liters of solution—the bread-and-butter concentration unit in general chemistry.
Mass = Molarity × Volume × Molecular Weight
Volume = Mass / (Molarity × Molecular Weight)
Molarity = Mass / (Volume × Molecular Weight)
Example: to make 500 mL of 0.1 M NaCl (MW ≈ 58.44 g/mol): mass = 0.1 × 0.5 × 58.44 = 2.92 g. Dissolve in less than 500 mL water, then dilute to the mark in a volumetric flask.
Standard Units Reference
- Molarity: M (mol/L) or mM (mmol/L)
- Volume: Liters (L) or Milliliters (mL)
- Mass: g, mg, or kg
- Formula weight: g/mol (same numeric value as molar mass)
Frequently Asked Questions
What is the difference between molarity and molality?
Molarity (M) is moles of solute per liter of solution. Molality (m) is moles of solute per kilogram of solvent. This calculator uses molarity only—standard for most general chemistry lab work.
Where do I get the molecular weight?
Use the value printed on the reagent bottle, your periodic table, or enter the chemical formula in our Molecular Weight Calculator for an automatic molar mass.
Does this account for solution density?
No. It assumes volume equals the final solution volume you enter. For concentrated acids or non-ideal solutions where volume changes on mixing, use manufacturer dilution tables or gravimetric methods.
What does the Calculate dropdown control?
Choose Mass, Volume, or Molarity. Formula Weight is always required; the unknown field hides while you enter the other two with their unit selectors.
Can I enter molarity in millimolar?
Yes. Select Millimolar (mM) in the Molarity unit dropdown. Volume accepts Liters or Milliliters; mass accepts g, mg, or kg.