What is the formula used?

moles = mass (g) / molar mass (g/mol). The molar mass is the mass of one mole of a substance, numerically equal to its relative atomic or molecular mass expressed in g/mol.

Where do I find the molar mass of a substance?

For elements, it is the atomic weight from the periodic table. For compounds, add up the atomic weights of all atoms in the molecular formula. The preset list in this tool contains standard values for many common substances.

What if I need to go from moles back to grams?

Rearrange the formula: grams = moles x molar mass. Multiply the number of moles by the molar mass to get the mass in grams.

Why are my results slightly different from textbook answers?

Minor differences arise from rounding in the molar masses used. This calculator uses values to two decimal places. Textbooks sometimes use rounded atomic weights (e.g. C = 12 instead of 12.01).

Can I use this for ionic compounds?

Yes. Enter the formula mass of the ionic compound in the molar mass field. For example, NaCl has a formula mass of 58.44 g/mol (Na 22.99 + Cl 35.45).

Grams to Moles Calculator

Name: Grams to Moles Calculator
Availability: InStock
Author: Nham Vu

Enter a mass in grams and a molar mass (g/mol) — or pick a common substance — to calculate the number of moles instantly.

Conversion Inputs

Common substance (optional)

Mass (grams)

Molar mass (g/mol)

Tip: select a substance above to auto-fill.

Enter a mass and molar mass, then click Calculate.

Quick reference — common molar masses

Substance	Formula	g/mol
Water	H2O	18.015
Carbon dioxide	CO2	44.010
Sodium chloride	NaCl	58.440
Glucose	C6H12O6	180.160
Sulfuric acid	H2SO4	98.079
Ammonia	NH3	17.031
Ethanol	C2H5OH	46.069
Calcium carbonate	CaCO3	100.087

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Summary

Enter a mass in grams and a molar mass (g/mol) — or pick a common substance — to calculate the number of moles instantly.

How it works

Enter the mass of your sample in grams.
Either select a substance from the preset list to auto-fill its molar mass, or type the molar mass in g/mol manually.
The calculator divides the mass by the molar mass to give moles.
The formula and intermediate values are displayed below the result.

Use cases

Determine the number of moles in a weighed sample before a chemical reaction.
Cross-check reagent quantities when preparing solutions of a known molarity.
Help students verify stoichiometry calculations from a chemistry textbook.
Quickly convert bulk measurements in a lab to moles for yield calculations.
Check mole quantities when scaling up or down a synthesis procedure.

Frequently Asked Questions

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Last updated: 2026-05-28 · Reviewed by Nham Vu