Molarity Calculator
Enter the mass of your solute, its molar mass and the total solution volume to find the molarity in moles per liter.
Molarity is the number of moles of solute per liter of solution. Convert mass to moles by dividing by the molar mass, then divide by the volume in liters. Dissolving 58.44 g of NaCl (molar mass 58.44 g/mol) in enough water to make 1 liter gives exactly 1 mole in 1 liter, or 1.0 M.
How to Use This Calculator
Enter three values: the mass of the solute you are dissolving (in grams), the solute's molar mass (in grams per mole), and the total volume of the finished solution (in liters). The calculator converts the mass to moles and divides by the volume to give molarity in mol/L, written with a capital M.
If you do not know the molar mass of your compound, calculate it first from the chemical formula — table salt (NaCl) is 58.44 g/mol, glucose (C₆H₁₂O₆) is 180.16 g/mol. Be careful with volume: molarity uses the volume of the final solution, not the volume of solvent you started with. In practice you dissolve the solute and then top up to the target volume in a volumetric flask.
How the Calculation Works
Molarity answers 'how many moles of solute are in each liter of solution?' It takes two steps. First convert mass to moles: moles = mass ÷ molar mass, because the molar mass is the grams contained in one mole. Then divide the moles by the solution volume in liters: molarity = moles ÷ liters. Combining them, M = mass ÷ (molar mass × volume in L). Concentration is an intensive property — it does not depend on how much solution you have, only on the ratio of solute to volume.
Worked Example
Suppose you dissolve 58.44 g of sodium chloride and make it up to 1.0 liter of solution. Sodium chloride has a molar mass of 58.44 g/mol, so moles = 58.44 ÷ 58.44 = 1.00 mol. Molarity = 1.00 mol ÷ 1.0 L = 1.0 M. If instead you had used 29.22 g in 0.5 L, you would get 0.5 mol ÷ 0.5 L = 1.0 M — the same concentration, because both the solute and the volume were halved.
What the Result Means
A 1.0 M solution contains one mole of dissolved substance in every liter. Molarity is the workhorse concentration unit in chemistry because reactions happen mole-for-mole, so knowing the molarity lets you measure out a precise number of moles simply by measuring a volume. To get a target number of moles, multiply molarity by the volume you dispense. Note that molarity changes slightly with temperature, since the volume of a liquid expands and contracts — for temperature-independent work, chemists sometimes use molality (moles per kilogram of solvent) instead.
Assumptions and Limitations
This calculation assumes the solute fully dissolves and that you are measuring the total solution volume, not the solvent volume alone. It does not account for volume changes on mixing (dissolving some solutes slightly changes the final volume) or for temperature effects on volume. For very concentrated solutions or gases dissolved under pressure, more careful methods are needed. The result is only as accurate as the molar mass and volume you provide.
When to Use a Molarity Calculator
Chemistry students and lab technicians use this to find molar concentration from the mass of solute, its molar mass, and the solution volume. Run it when preparing a solution to a target molarity or checking a concentration for a lab. Enter the three values to get molarity in mol/L.
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Open calculator →Frequently Asked Questions
What is molarity in simple terms?
Molarity is how concentrated a solution is, measured as the number of moles of dissolved substance per liter of solution. A 2 M solution has twice as many moles per liter as a 1 M solution.
How do I calculate molarity from grams?
Divide the grams of solute by its molar mass to get moles, then divide the moles by the solution volume in liters. In one step: molarity = grams ÷ (molar mass × liters).
Is molarity the same as concentration?
Molarity is one specific way of expressing concentration — moles per liter. Other concentration units include molality (moles per kg solvent), mass percent, and parts per million. Molarity is the most common in reaction chemistry.
Do I use solvent volume or solution volume?
Always the final solution volume. Dissolve the solute first, then add solvent up to the target volume. Using only the solvent volume gives a slightly wrong, higher concentration.
What does the capital M mean?
Capital M is the symbol for molar, meaning moles per liter. So '0.5 M HCl' reads as a 0.5 molar hydrochloric acid solution — half a mole of HCl per liter.
How is molarity different from molality?
Molarity is moles per liter of solution and changes slightly with temperature. Molality is moles per kilogram of solvent and does not, which makes it preferable for work across a range of temperatures.
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