Molarity Calculator
Calculate solution molarity from mass, volume, and molecular weight.
Supports 9 mass units, 8 volume units, 7 concentration scales, and 7 molarity units.
Updated August 30, 2026
What is molarity?
Molarity (also called molar concentration) measures how many moles of a dissolved substance exist in one liter of solution. It is the most common way to express concentration in chemistry labs because it directly ties the volume you measure in a graduated cylinder or volumetric flask to the number of molecules or ions available for reaction.
In short: a 1 molar (1 M) NaCl solution contains exactly one mole of sodium chloride — about 58.44 g — dissolved in enough water to make one liter of total solution.
Molarity matters because chemical reactions depend on thenumber of particles, not just their mass. Two solutions can have the same mass concentration (grams per liter) but very different molarities if the solutes have different molecular weights. This calculator lets you work with both perspectives — mass concentration and molarity — and convert between them instantly.
How to use this calculator
The calculator connects five quantities through two independent relationships. You enter any three values and it solves for the remaining two automatically.
Pick the fields you know
Enter values for at least three of the five fields: mass, molecular weight, volume, concentration, or molarity. You can change units at any time using the dropdowns.
Leave the unknown fields blank
The calculator determines which values can be derived from your inputs and computes them. Fields shown in blue are auto-calculated results.
Read the result and interpret
The solved values update in real time. Switch units to match your recipe, protocol, or textbook without recalculating by hand.
Worked example — preparing a sodium chloride solution
A lab protocol calls for 500 mL of 0.15 M NaCl (physiological saline). You know the molecular weight of NaCl is 58.44 g/mol. How much NaCl do you weigh out?
Enter three known values: volume = 500 mL, molarity = 0.15 M, molecular weight = 58.44 g/mol. The calculator derives mass and concentration.
Weigh out 4.38 g of NaCl, dissolve it in distilled water, and bring the total volume to exactly 500 mL. The calculator also shows the mass concentration is 8.77 g/L.
Formulas and variables
Two independent relationships connect the five quantities. The calculator uses both simultaneously, so providing any three values is enough to determine the other two.
Relationship 1 — Mass concentration
Mass concentration is simply the mass of solute divided by the total volume of solution:
Relationship 2 — Molar concentration
Molarity links concentration to molecular weight through the number of moles per liter:
Since both relationships share the concentration variable, you can bridge between mass-based and mole-based calculations in a single step. For example, given mass, volume, and molecular weight, the calculator finds both concentration and molarity.
Variable reference
| Symbol | Quantity | Default unit |
|---|---|---|
| Mass of solute | g | |
| Molecular weight of solute | g/mol | |
| Total volume of solution | L | |
| Mass concentration | g/mL | |
| Molarity (molar concentration) | M |
Bidirectional solving
Because the two relations share concentration, you can enter any three of the five quantities and the calculator solves for the remaining two. For instance, if you know the mass, molecular weight, and volume, it gives you both concentration and molarity. If you know concentration and molarity, it derives the molecular weight.
Real-world examples
Physiological saline
Normal saline for IV drips is 0.9% NaCl by mass, which corresponds to approximately 0.154 M. This calculator helps you convert between the mass-based and molar descriptions.
Dilute hydrochloric acid
A 0.1 M HCl solution is common in titrations. With a molecular weight of 36.46 g/mol, the mass concentration works out to:
Reverse calculation
A chemist measures a concentration of 49.04 g/L and knows the solute is sulfuric acid (98.08 g/mol). What is the molarity?
Tips and common mistakes
Watch the concentration units
The default concentration unit is g/mL, which is 1000× larger than g/L. Always check the unit dropdown — a reading of "1" in g/mL means 1000 g/L, not 1 g/L.
Volume means total solution volume
Molarity is defined as moles of solute per liter of total solution, not per liter of solvent. When you dissolve 58.44 g of NaCl in water, the final volume must be exactly 1 L — the water you add will be slightly less than 1 L because the salt occupies space.
Know your molecular weight
For compounds with hydration (e.g., CuSO₄·5H₂O), use the molecular weight of the full hydrate, not just the anhydrous salt. The water molecules are part of the crystal and affect how much mass you weigh out.
Molarity changes with temperature
Because solution volume expands and contracts with temperature, molarity is temperature-dependent. A 1.000 M solution at 20 °C will be slightly less than 1 M at 50 °C. For temperature-critical work, consider molality instead.
Limitations
•Ideal solution assumption. This calculator uses the standard molarity definition and does not account for non-ideal behavior such as activity coefficients, ion pairing, or volume changes upon mixing. For concentrated or electrolyte solutions, actual molarities may deviate from the calculated values.
•Temperature sensitivity. Molarity depends on solution volume, which changes with temperature. The calculator does not apply thermal expansion corrections. For precise work at non-ambient temperatures, measure volume at the temperature of use or switch to molality-based calculations.
•Positive values only. Molecular weight, volume, concentration, and molarity must be greater than zero. Mass can be zero (representing pure solvent). The calculator does not handle negative or undefined inputs.
•Not for preparation of dangerous solutions. Always follow proper laboratory safety procedures and consult published protocols when preparing concentrated acids, bases, or hazardous chemical solutions. This tool is for calculation assistance, not a substitute for validated laboratory procedures.
Related: Try our Grams to Moles Calculator → to convert between mass and moles, or the Molar Mass Calculator → to look up the molecular weight of common compounds.
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