Molecular Weight & Molarity Calculator

Convert between mass, moles, molarity, and volume — calculate exactly how much solute you need for any molar solution in the lab.

Chemical Formula

Try:

Molecular Weight

0.000 g/mol

Calculation Breakdown

Element	Atomic Mass	Atoms	Total	%

Total Molecular Weight

Elements in this compound

In formula

Other elements

Quick Examples

Click any compound to calculate its molecular weight instantly.

Water

H₂O

18.015 g/mol

Carbon Dioxide

CO₂

44.009 g/mol

Sodium Chloride

NaCl

58.443 g/mol

Glucose

C₆H₁₂O₆

180.156 g/mol

Ethanol

C₂H₅OH

46.069 g/mol

Sulfuric Acid

H₂SO₄

98.077 g/mol

How to Use the Molecular Weight & Molarity Calculator

To convert between mass, moles, and molarity, start by entering a chemical formula to determine the compound's molecular weight. Then use that molecular weight to calculate how many grams you need for a specific molar concentration, or find the molarity of a solution you've already prepared.

Follow these 5 steps for solution preparation calculations:

Enter the chemical formula of your solute (e.g., NaCl, KMnO₄, C₆H₁₂O₆) into the calculator and click "Calculate" to determine the molecular weight in g/mol.
Note the molecular weight value. This is the conversion factor between grams and moles for your specific compound.
To find mass needed for a molar solution: multiply the desired molarity (M) by the final volume in liters (L) by the molecular weight (g/mol). Mass (g) = M × V × MW.
To find the molarity of an existing solution: divide the mass of dissolved solute (g) by the molecular weight (g/mol) to get moles, then divide by the solution volume in liters. Molarity = mass ÷ (MW × V).
Adjust for desired concentration units. Convert between M, mM, and µM by moving the decimal: 1 M = 1,000 mM = 1,000,000 µM.

This calculator is built for lab technicians preparing buffer solutions, researchers making reagent stocks, pharmacology students calculating drug concentrations, and anyone performing solution chemistry where precise molarity matters.

How the Molecular Weight & Molarity Calculator Works

The molecular weight and molarity calculator connects 4 variables through 2 equations. Molecular weight links mass to moles. Molarity links moles to solution volume. By knowing any 3 variables, you can solve for the 4th.

The core equations and their applications:

Mass-to-Moles Conversion

n = mass (g) ÷ MW (g/mol). This converts a mass reading from the balance into the number of moles of substance. MW serves as the conversion factor.

Molarity Equation

Molarity (M) = n (mol) ÷ V (L). Concentration in moles per liter. Combine with the mass equation: M = mass ÷ (MW × V).

Gram Calculation

mass (g) = M × V (L) × MW (g/mol). Tells you exactly how many grams to weigh for a target solution. Most common use case for lab preparation.

C₁V₁

Dilution Equation

C₁V₁ = C₂V₂. For diluting stock solutions to working concentrations. Solve for V₁ to find how much stock to use: V₁ = (C₂ × V₂) ÷ C₁.

Worked example: Prepare 500 mL of 0.5 M sulfuric acid (H₂SO₄, MW = 98.079 g/mol). mass = 0.5 M × 0.5 L × 98.079 g/mol = 24.52 g. Carefully add 24.52 g of H₂SO₄ to water and bring the total volume to 500 mL. Always add acid to water, not water to acid.

These calculations are used daily in chemistry, biology, and medical laboratories for buffer preparation (PBS, TBS, HEPES), reagent stocks (staining solutions, fixatives), media preparation (bacterial culture media), and drug formulation (converting between mg/mL and molar concentrations for pharmacological studies).

Common Compound Molecular Weights

Reference table of frequently searched chemical compounds.

Chemical Formula	Compound Name	Molecular Weight
H₂O	Water	18.015 g/mol
CO₂	Carbon Dioxide	44.009 g/mol
NaCl	Sodium Chloride	58.443 g/mol
NH₃	Ammonia	17.031 g/mol
CH₄	Methane	16.043 g/mol
H₂SO₄	Sulfuric Acid	98.077 g/mol
CaCO₃	Calcium Carbonate	100.086 g/mol
C₆H₁₂O₆	Glucose	180.156 g/mol
C₂H₅OH	Ethanol	46.069 g/mol
HCl	Hydrochloric Acid	36.461 g/mol
NaOH	Sodium Hydroxide	39.997 g/mol
Ca(OH)₂	Calcium Hydroxide	74.092 g/mol
HNO₃	Nitric Acid	63.012 g/mol
KMnO₄	Potassium Permanganate	158.032 g/mol
CuSO₄	Copper(II) Sulfate	159.607 g/mol

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Molecular Weight & Molarity Calculator FAQs and Common Questions

Answers to common questions about molarity calculations, solution preparation, unit conversions, and dilution formulas.

How do I calculate molarity from molecular weight and mass?

To calculate molarity from molecular weight and mass: first convert mass to moles using moles = mass (g) ÷ molecular weight (g/mol). Then divide moles by solution volume in liters: Molarity (M) = moles ÷ volume (L). For example, dissolving 5.85 g of NaCl (MW = 58.44 g/mol) in 500 mL of water gives: 5.85 ÷ 58.44 = 0.1 mol, and 0.1 mol ÷ 0.5 L = 0.2 M solution.

What is the relationship between molecular weight and molarity?

Molecular weight connects mass and moles: moles = mass ÷ molecular weight. Molarity connects moles and volume: M = moles ÷ volume (L). Together, these relationships form the equation: Molarity = mass (g) ÷ [molecular weight (g/mol) × volume (L)]. Molecular weight is the conversion factor that bridges between the grams you weigh on a balance and the molar concentration of your solution.

How do I calculate how many grams I need for a specific molar solution?

Use the formula: mass (g) = Molarity (M) × volume (L) × molecular weight (g/mol). To make 250 mL of a 1 M glucose solution (MW = 180.16 g/mol): mass = 1 × 0.25 × 180.16 = 45.04 g. Weigh 45.04 g of glucose and dissolve in enough solvent to reach a final volume of 250 mL.

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. Molarity changes with temperature because solution volume changes with temperature. Molality does not change with temperature because it uses mass (kg) instead of volume. Use molarity for most routine lab work; use molality for colligative property calculations (boiling point elevation, freezing point depression).

How do I dilute a stock solution to a target molarity?

Use the dilution equation: C₁V₁ = C₂V₂, where C₁ is the stock concentration, V₁ is the volume of stock needed, C₂ is the target concentration, and V₂ is the final solution volume. To make 100 mL of 0.1 M HCl from a 1 M stock: V₁ = (0.1 × 100) ÷ 1 = 10 mL. Take 10 mL of the 1 M stock and add solvent to reach 100 mL total.

Can I use this calculator for millimolar (mM) or micromolar (µM) concentrations?

Yes. The calculator works with any concentration unit when you convert consistently. 1 mM = 0.001 M, and 1 µM = 0.000001 M. Enter values in molar (M) for calculation, then convert the result: a 0.005 M solution equals 5 mM. For mass at micro-scale: mass (mg) = Molarity (mM) × volume (mL) × molecular weight (g/mol) ÷ 1000.