Molarity Calculator
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What Your Result Means
- Molarity (M): The number of moles of solute per liter of solution. A 1 M solution contains one mole of solute in every liter. Higher molarity means a more concentrated solution.
- Millimolarity (mM): Molarity expressed in thousandths — useful for dilute solutions common in biology and biochemistry where concentrations are typically in the micromolar to millimolar range.
- Amount in mmol: The total millimoles of solute you have, regardless of volume. This helps when you need to know how much substance is available for a reaction.
How This Calculator Works
You enter the moles of solute and the volume of solution in liters, milliliters, or microliters. The tool converts the volume to liters, then divides moles by liters to get molarity (M). It also reports millimolarity (M × 1,000) and the total amount in millimoles (moles × 1,000). It assumes a homogeneous solution at standard conditions and does not account for activity coefficients or temperature effects.
Quick 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. Molality doesn't change with temperature because mass doesn't expand, while molarity can shift slightly as the solution's volume changes with temperature.
Can I use this for dilution calculations?
This calculator finds molarity from moles and volume. For dilutions, use the formula C₁V₁ = C₂V₂ — multiply your starting concentration by starting volume to get the moles, then divide by the new volume.
How do I convert grams to moles?
Divide the mass in grams by the substance's molar mass (g/mol). For example, 58.44 g of NaCl ÷ 58.44 g/mol = 1 mol. Use the molecular weight calculator to find the molar mass.
Why does the volume unit matter?
Molarity is defined per liter. If you measure volume in milliliters or microliters, the calculator converts to liters first. Entering 500 mL is the same as 0.5 L — the result is the same, but forgetting to convert is a common lab error.
Sources
- Wikipedia — Molar Concentration (definition, units, related measures)
- Khan Academy — Molarity (worked examples and dilution calculations)
Method & review
Estimate only. Results reflect your inputs and standard formulas. Double-check important decisions independently.