Grams to Moles Calculator
Calculate grams moles with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Reviewed by Manoj Kumar, Mathematics Educator
Formula
n = m / M (moles = grams / molar mass)
Moles equal mass divided by molar mass. To reverse, mass equals moles times molar mass. The molar mass is the sum of atomic masses of all atoms in the chemical formula, found on the periodic table.
Worked Examples
Example 1: Grams of NaCl to Moles
Problem:Convert 117 g of sodium chloride (NaCl, M = 58.44 g/mol) to moles.
Solution:n = mass / molar mass\nn = 117 / 58.44\nn = 2.0014 mol\nParticles = 2.0014 * 6.022e23 = 1.205e24
Result:2.001 moles of NaCl (1.205 x 10^24 formula units)
Example 2: Moles of Glucose to Grams
Problem:How many grams are in 0.25 moles of glucose (C6H12O6, M = 180.16 g/mol)?
Solution:mass = moles * molar mass\nmass = 0.25 * 180.16\nmass = 45.04 g
Result:45.04 grams of glucose
Frequently Asked Questions
How do you convert grams to moles?
To convert grams to moles, divide the mass in grams by the molar mass (molecular weight) in grams per mole: moles = grams / molar mass. The molar mass is found by adding up the atomic masses of all atoms in the chemical formula from the periodic table. For example, water (H2O) has a molar mass of 2(1.008) + 16.00 = 18.015 g/mol, so 36 grams of water is 36/18.015 = 2.0 moles. This conversion is the foundation of all stoichiometric calculations in chemistry.
What is the relationship between moles, mass, and particles?
These three quantities are connected through molar mass and Avogadro's number. Mass and moles are related by: n = m/M. Moles and particles are related by: N = n * NA (6.022e23). Therefore particles and mass are related by: N = (m/M) * NA. One mole of any substance always contains 6.022e23 particles but has different masses depending on the molar mass. One mole of hydrogen gas (2 g) and one mole of lead (207 g) both contain the same number of atoms but differ greatly in mass.
Why do students most often get a grams-to-moles conversion wrong?
The most common mistake is using the wrong molar mass — plugging in a reactant's molar mass when the problem calls for a product's, or forgetting to include water of hydration in a hydrate's formula mass. The second most common error is a decimal or exponent slip when reading atomic masses off the periodic table (mixing up 12.01 for carbon with 12.00, for instance), which introduces small but compounding errors across multi-step stoichiometry problems. Always write out the units explicitly (g ÷ g/mol = mol) as a sanity check that they actually cancel correctly.
How is grams-to-moles conversion used when preparing a lab solution?
Before making any molar solution, a chemist first decides the target concentration and volume (for example, 250 mL of 0.5 M NaOH), calculates the moles needed (0.125 mol), then uses this exact grams-to-moles relationship in reverse to find the mass to weigh out: 0.125 mol x 40.00 g/mol = 5.00 g of NaOH. That mass is weighed on an analytical balance, dissolved in a small volume of solvent, then diluted to the full 250 mL mark in a volumetric flask — a workflow repeated in essentially every wet-chemistry lab before a titration, synthesis, or standardization procedure.
References
Reviewed by Manoj Kumar, Mathematics Educator · Editorial policy