Please provide any three values in the fields below to calculate the fourth value in the molarity equation.
Molarity = Mass / (Molecular Weight × Volume)
Molarity is just a fancy word for concentration. It tells you how much of a substance (called the solute) is dissolved in a liquid (called the solvent). Think of it like this:
If you put one spoonful of sugar in a cup of tea, that's a certain concentration. If you put five spoonfuls, that's a much stronger concentration. Molarity is just a precise way to measure that.
The official definition? Molarity is the number of moles of solute per liter of solution. A mole is just a counting unit in chemistry, like a dozen eggs, but way bigger. One mole equals about 6.02 × 10²³ particles. That's a lot of particles.
M = n / V
M = molarity (mol/L) | n = moles of solute (mol) | V = volume of solution (L)
Sounds confusing? Let's say you have 2 moles of salt dissolved in 1 liter of water. Your molarity is 2 M ("2 molar"). Easy, right?
But what if you don't know the number of moles? No problem. You can find moles from the mass:
n = mass / molar mass
So the full formula: M = (mass of solute) / (molar mass × volume in L)
That's what our calculator does automatically. You give it mass, molar mass, and volume. It spits out molarity.
Using our calculator is dead simple. Here's a step-by-step example:
🧂 Example: Making a Salt Water Solution
You have 58.44 grams of NaCl (table salt) dissolved in enough water to make 1 liter. What's the molarity?
Enter the mass: 58.44 grams
Enter the molar mass of NaCl: 58.44 g/mol (Na = 22.99 + Cl = 35.45)
Enter the volume: 1 liter
Click calculate → Answer: 1 M (a 1 molar salt water solution)
See how easy that was? No algebra required.
Mistake #1: Forgetting to Convert mL to L
The formula uses liters, but problems often give mL. 500 mL = 0.5 L. Divide by 1000. Always. Our calculator handles this, but if doing manually, don't forget!
Mistake #2: Confusing Molarity with Molality
Molarity (M) = moles per liter of <strong>solution</strong>. Molality (m) = moles per kg of <strong>solvent</strong>. Molarity changes with temperature. Molality doesn't.
Mistake #3: Using the Wrong Molar Mass
Use the molar mass of the compound, not just one element. NaCl = 58.44 g/mol, not 22.99 (sodium alone). Double-check your periodic table.
Mistake #4: Not Accounting for Hydrates
Some compounds come with water attached (like CuSO₄·5H₂O). That water adds mass — include it in your molar mass calculation.
Biologists and chemists need precise concentrations for experiments. PCR tests (like COVID-19) require exact molarities of primers and enzymes. Too much or too little and the test won't work.
Pharmacists use molarity for IV solutions. A saline drip needs to be exactly 0.9% NaCl, about 0.154 M. Wrong concentration could hurt the patient.
Factories making cleaning products, fertilizers, or food need consistent concentrations. Molarity ensures every batch is identical.
Sometimes you have a concentrated stock solution and need to make it weaker. The formula is:
M₁V₁ = M₂V₂
M₁ = stock concentration | V₁ = volume to take | M₂ = desired concentration | V₂ = final volume
📊 Example:
You have 2 M HCl and need 500 mL of 0.5 M HCl. How much stock do you use?
Take 125 mL of 2 M solution, add water to make 500 mL total. Our calculator's dilution mode handles this.
Not everything dissolves in water. If you try to make a 2 M solution of something that only dissolves up to 0.5 M, you'll have undissolved solid sitting at the bottom. That's not a real solution. Always check solubility before starting. Most textbooks have a solubility table — or just Google it.
Weigh out your solute accurately
Dissolve it in a small amount of solvent (about half the final volume)
Pour into a volumetric flask
Add more solvent until you reach the mark on the flask
This ensures exact volume. If you just add solute to the full volume, the final volume might be slightly off.
Ever wonder where "molarity" comes from? It's based on "mole," introduced by German chemist Wilhelm Ostwald in the late 1800s. The mole concept made chemistry way easier — it let scientists count atoms and molecules by weighing them.
Before molarity, chemists used "normality" and "equivalent weight." Those are still used sometimes, but molarity is the standard now. It's simpler and more universal.
Which one should you use? For most chemistry classes, molarity is the go-to.
Problem: Molarity is super small (0.0001 M)
Solution: Possible with tiny solute or huge volume. Double-check units — did you use grams instead of kg? Or mL instead of L?
Problem: Molarity is huge (100 M)
Solution: Probably impossible — most compounds don't dissolve that well. Check molar mass. Did you forget to convert grams to moles?
Problem: You get an error message
Solution: Make sure you entered numbers in all fields. The calculator can't work with blanks.
Using our calculator on your phone? No problem. It's fully responsive. Just tap the fields and type. The buttons are big enough for your thumbs.
Pro tip: If you're in the lab and your hands are dirty, use the voice input feature on your phone's keyboard. Say "fifty-eight point four four" instead of typing.
Given the mass of the solute, moles can be calculated by dividing mass by molecular weight:
M = m / (MW × V)
m = mass (g), MW = molecular weight (g/mol), V = volume (L)
Example: 10 g NaCl in 0.5 L water (MW = 58.44 g/mol)
M = 10 / (58.44 × 0.5) = 0.342 M
Number of moles of solute per liter of solution.
SI unit. 1 mole = 6.02214076 × 10²³ particles (Avogadro number).
Substance present in largest quantity that dissolves the solute.
Any substance mixed into a solvent — gas, liquid, or solid.
Mass of 1 mole of a substance, typically in g/mol.
Often used interchangeably with molar mass; technically unitless.
Molarity (M) is moles of solute per liter of solution. Molality (m) is moles of solute per kilogram of solvent. Molarity changes with temperature because liquids expand. Molality stays the same. Use molarity for most lab work.
First, find moles by dividing mass by molar mass. Then divide by volume in liters. Formula: M = (mass / molar mass) / volume in L. Our calculator does this in one click.
The definition uses liters. 250 mL = 0.25 L — divide by 1000. Forgetting this is the most common student mistake.
Yes, as long as you know the molar mass. Find it on the periodic table or Google it. Works for any compound — salt, sugar, acids, bases, anything.
1 M means "1 molar" — 1 mole of solute per liter of solution. A 1 M NaCl solution has 58.44 grams of salt per liter of water.
You need 0.5 moles per liter. NaCl molar mass = 58.44 g/mol, so 29.22 grams (half). Dissolve in enough water to make 1 liter. Use a volumetric flask for accuracy.
About 55.5 M. 1 liter of water weighs 1000g, molar mass = 18.015 g/mol. 1000 ÷ 18.015 = 55.5 moles/L. But we usually don't talk about water's molarity as a solvent.
Use M₁V₁ = M₂V₂. M₁ = stock concentration, V₁ = volume to take, M₂ = desired concentration, V₂ = final volume. Solve for V₁, then add solvent to reach V₂.
Not all compounds dissolve well. Check solubility first. If not fully soluble, you can't make that concentration. Try a lower concentration or different solvent.
Molarity is one type of concentration. Concentration is a general term. Molarity is the most common measure in chemistry. Others include molality, normality, and percent concentration.