Molar Mass Calculator

Effortlessly compute moles, mass, or molar mass using the fundamental formula n = m / M. Perfect for stoichiometry, lab preparation, and chemistry homework. Supports multiple mass units (g, mg, kg) with automatic conversion.

Enter values and click Calculate

Understanding the Mole Concept and Molar Mass Calculations

The molar mass (M) of a substance is the mass of one mole of that substance, expressed in g/mol. Using the relationship: Moles (n) = Mass (m) / Molar mass (M), Mass (m) = Moles (n) × Molar mass (M), Molar mass (M) = Mass (m) / Moles (n). You can solve for any variable when the other two are known. This calculator automates these calculations, converts between grams, milligrams, and kilograms, and rounds results to a suitable precision. Ideal for preparing solutions, converting recipe amounts, or verifying experimental data.

Formula

n = \frac{m}{M} \qquad m = n \times M \qquad M = \frac{m}{n}

How to Use?

Select what you want to calculate: moles, mass, or molar mass.
Enter the two known quantities. If solving for moles, enter mass and molar mass; for mass, enter moles and molar mass; for molar mass, enter mass and moles.
Use the unit dropdowns to choose the correct mass unit (g, mg, kg) – the calculator automatically converts to grams for the calculation.
Read the result with its appropriate unit.

Worked Examples

Calculate moles from mass and molar mass

Given:inputs

Solve for:Moles n = m / M

Mass (m):5.0

Mass unit:g

Molar Mass M (g/mol):18.02

Result:calculated

Result:0.2775 mol

Calculate mass from moles and molar mass

Given:inputs

Solve for:Mass m = n × M

Moles n (mol):0.5

Molar Mass M (g/mol):58.44

Result:calculated

Result:29.22 g

Calculate molar mass from mass and moles

Given:inputs

Solve for:Molar mass M = m / n

Mass (m):100.0

Mass unit:g

Moles n (mol):2.5

Result:calculated

Result:40 g/mol

The Mole: A Counting Unit in Chemistry

A mole (mol) is 6.022×10²³ particles (Avogadro’s number). The molar mass of an element or compound tells you how many grams are in one mole. For example, carbon-12 has a molar mass of exactly 12 g/mol, so 12 g of carbon contains one mole of atoms.

Why Convert Mass Units?

In the lab, you might measure in milligrams for small samples or kilograms for bulk quantities. This calculator automatically converts all mass inputs to grams using the built‑in unit conversions, ensuring the result is accurate regardless of the original unit.

Practical Applications

Use the molar mass calculator to: determine how many moles are in a given sample for a reaction; find the mass of a compound needed to obtain a specific number of moles; or experimentally determine the molar mass of an unknown substance from mass and mole data.

Table: Examples of Molar Mass Calculations

Substance	Mass	Molar Mass (g/mol)	Moles
Sodium chloride (NaCl)	58.44 g	58.44	1.000 mol
Glucose (C₆H₁₂O₆)	180.16 g	180.16	1.000 mol
Water (H₂O)	36.04 g	18.02	2.000 mol

FAQs

What is the difference between molar mass and molecular weight?

Molar mass is numerically equal to molecular weight but expressed in grams per mole. Molecular weight is a dimensionless quantity representing the sum of atomic masses. For practical chemistry, they are used interchangeably.

Can I calculate the molar mass of a compound without entering a formula?

Yes – this calculator only needs numeric values. For molar mass of a compound, you would typically look it up or compute it from the periodic table, then enter the number. For formula‑based molar mass, see our molecular weight calculator (if available).

Why are the results rounded differently for moles and mass?

Moles often need higher precision (6 decimals) because they are used in stoichiometric calculations, while mass (4 decimals) is usually sufficient for lab measurements.