Science & Lab

💧

Molarity Calculator: Mass, Volume & Molecular Weight

Calculate molarity, mass, volume, or molecular weight. M = m/(MW×V). Common compounds.

⚙️

Settings

🔄

Calculate For

🧪

Common Compounds

Select a compound to auto-fill molecular weight, or enter manually below.

⚛️

Molecular Weight (MW)

⚖️

Mass of Solute

📦

Volume of Solution

Results
💧

Enter the known values to calculate

M

Information Hub

The Core Formula

M = molarity (mol/L), m = mass of solute (g), MW = molecular weight (g/mol), V = volume of solution (L).

Mass (g)÷(MW × V)=Molarity

Common Units

  • M = mol/L
  • mM = mmol/L
  • µM = µmol/L

Volume in L; mass in g; MW in g/mol.

Molarity vs Molality: Don’t Mix Them Up

Molarity is moles of solute per liter of solution. It depends on the total volume of the mixture (solute + solvent). When you add more solute or change temperature, the volume can change, so molarity can change.

Molality is moles of solute per kilogram of solvent only. It ignores the volume of the solute. Molality is temperature-independent and preferred for colligative properties (boiling-point elevation, freezing-point depression).

M=nVsolutionM = \frac{n}{V_{\text{solution}}}vsm=nmsolventm = \frac{n}{m_{\text{solvent}}}

This calculator uses molarity. For dilute aqueous solutions near room temperature, molarity and molality are often close—but they are not the same.

Molarity: Concentration from Mass, Volume & MW

Divide mass by (MW × volume) to get molarity—or rearrange to solve for mass, volume, or MW. Grab a compound from the search list to fill molecular weight, or type your own.

Core Concepts

The Formula

M=mMW×VM = \frac{m}{MW \times V}. Rearrange to get mass m=M⋅MW⋅Vm = M \cdot MW \cdot V, volume V=mM⋅MWV = \frac{m}{M \cdot MW}, or MW. All in base units: mol/L, g, g/mol, L.

Common Compounds

Type NaCl, HCl, NaOH, or glucose in the search box—selecting one fills molecular weight. Handy for quick setups; you can still edit the MW field.

Molarity vs Molality

Molarity: moles per liter of solution. Molality: moles per kilogram of solvent. Mix them up and your colligative-property numbers will be wrong.

Units Supported

Concentration: M, mM, µM, nM, mol/m³, plus g/L, mg/L, ppm, ppb. Mass: g, mg, kg, t, Da, lb, oz. Volume: L, mL, m³, cm³, gal, qt, pt, and more.

Molarity Calculator: Mass, Volume & Molecular Weight

Find molarity, mass, volume, or MW from the other three. Supports M, mM, µM, ppm, g/L. Common compounds included. No sign-up—runs in your browser.

How to Calculate Molarity

The defining equation is M=mMW×VM = \frac{m}{MW \times V}. You need mass mm in grams, molecular weight MWMW in g/mol, and volume VV in liters. Rearranging: mass m=M×MW×Vm = M \times MW \times V; volume V=mM×MWV = \frac{m}{M \times MW}; molecular weight MW=mM×VMW = \frac{m}{M \times V}. Toggle "Calculate For" to solve for whichever variable you don't know.

When Molarity and Molality Diverge

Molarity counts moles per liter of the whole mixture; molality counts moles per kilogram of solvent. Add more solute and the total volume grows—molarity drops a bit. Molality, based on solvent mass, doesn't care. For boiling-point elevation and freezing-point depression, textbooks use molality for that reason. In dilute aqueous work, the two are close enough that many lab protocols don't bother distinguishing.

Molarity Calculator FAQ

? How do I calculate molarity from mass and volume?

Plug into M=mMW×VM = \frac{m}{MW \times V}: mass in g, MW in g/mol, volume in L. Example—5.84 g NaCl (MW 58.44) in 1 L gives 0.1 M. Search for NaCl in the compound dropdown to fill MW, then enter mass and volume.

? What is the difference between molarity and molality?

Molarity divides by the total volume of the solution; molality divides by the mass of solvent only. Same solute, different denominators. At low concentration in water they're almost the same. At high concentration or when temperature swings, molarity shifts (volume changes) but molality holds steady.

? How do I make a 1 M NaCl solution?

Weigh 58.44 g NaCl and add water until the total volume is 1 L. Don't add 58.44 g to 1 L of water—the solute adds volume, so you'd end up slightly above 1 L and slightly under 1 M.

? Can I use ppm or g/L for concentration?

Yes. The calculator accepts both molarity units (M, mM, µM) and mass concentration (g/L, mg/L, ppm, ppb). For mass concentration it converts to mol/L using the molecular weight you enter.
🧪
Science & Lab Reference Note

Educational Use: These tools use standard scientific formulas and accepted constants. Results are intended for learning, homework, and general reference—not for regulated lab work, industrial processes, or clinical applications.

Verification Recommended: Real-world conditions (purity, temperature, pressure, humidity) affect outcomes. For research, manufacturing, or safety-critical work, confirm with a qualified professional or calibrated lab equipment.

Not Professional Advice: This site does not provide chemical, medical, or engineering advice. All calculations run locally in your browser; no data is stored or transmitted.

© 2026 CalcRegistry Reference Last Logic Update: FEB 2026Free Online Utility Tools