Moles to Grams Calculator
Converting an amount of substance in moles to a mass in grams is one of the most common steps in chemistry, whether you are preparing a solution, balancing a reaction or weighing out a reagent. The conversion rests on a single idea: the molar mass of a substance is the mass of exactly one mole of it, expressed in grams per mole. Multiply the number of moles by that molar mass and the mole unit cancels, leaving a mass in grams that you can read off a balance. This calculator takes the amount in moles and the molar mass of your compound, then returns the mass in grams to two decimal places. The molar mass is left fully editable because it depends on the chemical formula you are working with; you find it by adding the standard atomic weights of every atom in the formula, values published by the National Institute of Standards and Technology. There is no hidden table and no assumed substance, so the same tool serves water, glucose, sodium chloride or any pure compound. Every figure here is computed deterministically from the standard conversion formula, shown below, with a worked example that reconciles exactly to the calculator so you can follow each step yourself.
Mass equals the amount in moles times the molar mass: grams = moles x molar mass. At 0.5 mol of water with a molar mass of 18.015 g/mol, the mass is 9.01 g. The molar mass comes from the substance's chemical formula.
Moles to grams formula
m = n x M
m = mass in grams
n = amount of substance in moles
M = molar mass in grams per mole
The molar mass M is the mass of one mole of the substance. Multiplying the amount n (in moles) by M cancels the mole unit and leaves a mass in grams. To go the other way, divide a mass in grams by the molar mass to recover the amount in moles.
Worked example
You need to weigh out 0.5 mol of water (H2O), which has a molar mass of 18.015 g/mol.
- Identify the amount: n = 0.5 mol
- Identify the molar mass: M = 18.015 g/mol
- Multiply: m = 0.5 x 18.015 = 9.0075 g
- Round to two decimal places: m = 9.01 g
So 0.5 mol of water weighs 9.01 g. These are the calculator's default inputs, so the result above matches the widget exactly.
Molar masses of common substances
Molar mass is the sum of the standard atomic weights of the atoms in the formula.
| Substance | Formula | Molar mass (g/mol) |
|---|---|---|
| Water | H2O | 18.015 |
| Sodium chloride | NaCl | 58.44 |
| Glucose | C6H12O6 | 180.156 |
| Carbon dioxide | CO2 | 44.009 |
| Ethanol | C2H6O | 46.069 |
Standard atomic weights: US National Institute of Standards and Technology (NIST).
Moles to grams calculator: frequently asked questions
How do you convert moles to grams?
Multiply the amount of substance in moles by the molar mass of the substance in grams per mole. The molar mass cancels the mole unit and leaves a mass in grams. For example, 0.5 mol of water with a molar mass of 18.015 g/mol gives 0.5 x 18.015 = 9.01 g.
Where do I find the molar mass?
Add up the standard atomic weights of every atom in the chemical formula. The standard atomic weights are published by the National Institute of Standards and Technology (NIST) and IUPAC. For water (H2O) the molar mass is about 18.015 g/mol because hydrogen is about 1.008 and oxygen about 15.999 g/mol.
What is a mole?
A mole is the SI unit for amount of substance. One mole contains exactly 6.02214076 x 10^23 elementary entities, a value known as the Avogadro number. The mole links the number of particles to a measurable mass through the molar mass of the substance.
Does the calculator work for any compound?
Yes. The conversion mass = moles x molar mass holds for any pure substance. Just enter the correct molar mass for your compound. The molar mass is the only substance-specific input, so the same formula serves elements, molecules and ionic compounds alike.
What is the moles to grams formula?
Mass in grams = amount in moles x molar mass in grams per mole. To reverse the conversion, divide a mass in grams by the molar mass to get the amount in moles.
Official sources
- Standard atomic weights and the SI mole: US National Institute of Standards and Technology (NIST). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.