Molarity Calculator
Calculate the molarity (molar concentration) of a solution from solute mass, molar mass, and solution volume. Essential for chemistry lab work and solution preparation.
About this calculator
Molarity measures how concentrated a solution is: moles of dissolved solute per liter of total solution volume. This calculator starts from moles = solute mass (g) ÷ molar mass (g/mol), then divides by solution volume in liters to get molarity (M). From there it derives several other views of the same solution — millimoles, concentration in g/L and mg/mL, and molality (moles per kilogram of solvent). Molality is the piece most likely to trip you up: this tool approximates solvent mass by subtracting the solute mass from the solution volume converted to grams assuming a 1 g/mL density, essentially treating the solvent as water.
That's a rough shortcut, not water's actual behavior in a real mixed solution (dissolving salt in water doesn't just add a mass on top of a fixed volume) — treat the molality output as a directional estimate, not a lab-grade number, and don't skip a real gravimetric measurement for anything precision matters for. The table of mass needed for common target molarities (0.01M, 0.1M, 0.5M, 1M, 2M) is useful for prepping stock solutions: given a molar mass and target volume, it tells you how many grams to weigh out for the solution you actually want. The most common real-world mixup is molarity versus molality — molarity is per liter of solution (which changes with temperature as the solution expands or contracts), while molality is per kilogram of solvent and stays fixed regardless of temperature. If you're doing precise quantitative chemistry, be sure you know which one your protocol calls for.
Inputs
Results
Molarity
1 M
Moles of Solute
1 mol
How to Use This Calculator
- Enter solute mass (g) and molar mass (g/mol) to calculate moles of solute.
- Enter solution volume (L).
- Review molarity in mol/L (M) and moles of solute.
- To make a solution of known molarity: use the mass needed output to weigh the solute before adding solvent to volume.
- Check units carefully -- molarity is moles per liter, not per kg (which would be molality).
How the result changes with Molar Mass
| Molar Mass | Molarity | Moles of Solute |
|---|---|---|
| 29 | 2.0152 M | 2.0152 mol |
| 44 | 1.3282 M | 1.3282 mol |
| 88 | 0.6641 M | 0.6641 mol |
| 146 | 0.4003 M | 0.4003 mol |
What each input means
- Solute Mass
- Mass of the dissolved substance in grams (e.g., 58.44g of NaCl).
- Molar Mass
- Molar mass of the solute (e.g., NaCl = 58.44 g/mol, glucose = 180.16 g/mol).
- Solution Volume
- Total volume of the solution in liters.
What each result means
- Molarity
- Molar concentration (moles of solute per liter of solution).
- Molality
- Moles of solute per kilogram of solvent.
How this is calculated
Formula
Molarity (M) = moles / volume = (mass / molar mass) / volume. Where: moles = mass (g) / molar mass (g/mol), and volume is in liters.Worked example, using the default values
- Identify Input ParametersSolute Mass = 58.44, Molar Mass = 58.44, Solution Volume = 1 = 3 input(s) provided
- Calculate MolarityMolarity1 = 1
- Calculate Moles of SoluteMoles of Solute1 = 1
- Calculate MillimolesMillimoles1000 = 1000
- Calculate ConcentrationConcentration58.44 = 58.44
Engine last updated . Checked against 1 independently-derived test — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What's the difference between molarity and molality, and why do both appear in the results?
Molarity (M) is moles of solute per liter of total solution volume, which is what this calculator solves for directly from your inputs. Molality is moles per kilogram of solvent, and since the tool doesn't know your solvent's exact mass, it approximates it by assuming water density (1 g/mL) and subtracting the solute mass from the total solution volume in grams. That approximation ignores the volume changes that occur when substances actually dissolve, so treat the molality figure as directional rather than lab-exact.
How does the mass-needed table for different target molarities work?
For each listed target molarity (0.01M through 2.0M), the calculator multiplies your entered molar mass by your entered solution volume and by that target molarity value, giving the grams of solute you'd need to weigh out to hit that concentration at your chosen volume. It's the same M = moles/volume relationship rearranged to solve for mass, reused across five common targets so you can compare stock-solution options at a glance.
Why do millimoles and mg/mL show different precision than the other outputs?
Millimoles is just moles multiplied by 1000, and concentration in mg/mL is grams of solute per 1000 mL — both derived directly from the same solute mass and mole calculation as molarity, not independent measurements. They're rounded to different decimal places than molarity or moles purely because each output is rounded separately for display, not because the underlying math differs in precision.
Can I use this calculator for solutions other than water-based ones?
The molarity, moles, millimoles, and concentration outputs all work for any solvent since they only use solute mass, molar mass, and total solution volume. The molality output, however, assumes the solvent behaves like water at 1 g/mL density when estimating solvent mass, so it will be inaccurate for non-aqueous solvents with a different density — the other outputs stay solvent-independent.
Do I need to account for water of hydration in the molar mass?
Yes, if your solute is a hydrate. A hydrate like copper(II) sulfate pentahydrate (CuSO4·5H2O) has a different molar mass (249.68 g/mol) than the anhydrous form (CuSO4, 159.61 g/mol) — using the wrong one produces a molarity that's proportionally off even though the mass and volume you entered are both correct, since the calculator has no way to tell which molar mass you intended.
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