Convert grams to moles or moles to grams using molar mass, with particle count, worked-equation output, and quick chemistry reference masses.
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Mass ↔ moles chemistry worksheet Convert grams to moles or moles to grams with the molar mass in `g/mol`, then use the same result to estimate particle count and practical bench references such as the mass of `1 mmol`.
Quick chemistry examples
Molar mass must be positive Provide the mass or moles and the molar mass of the substance to convert between grams and moles. If you only know the formula, first calculate its molar mass on the molecular weight calculator.
Grams to moles converter: convert mass to moles with molar mass and particle count
The grams-to-moles converter translates a mass measurement into a mole quantity, or converts moles back into grams, for any substance with a known molar mass. It also estimates particle count with Avogadro's number and surfaces the bench shortcut that `1 mmol` has the same number in `mg` as the molar mass in `g/mol`.
The grams-to-moles formula
Moles equal mass divided by molar mass. If you have 36 grams of water (molar mass 18.015 g/mol), you have 36 / 18.015 ≈ 2.0 moles. In the reverse direction, multiplying moles by molar mass gives the mass in grams.
The number of individual particles (atoms, molecules, or formula units) is found by multiplying moles by Avogadro's number: 6.022 × 10²³ particles per mole.
moles = mass (g) / molar mass (g/mol)
Reverse: mass = moles × molar mass. This is the specific relationship the calculator applies when building the result.
particles = moles × 6.022 × 10²³
Avogadro's number converts moles to individual particles.
Finding the molar mass
The molar mass is the molecular weight expressed in grams per mole. For elements, it equals the atomic weight on the periodic table. For compounds, sum the atomic weights of all atoms in the formula. Use the molecular weight calculator on this site to find the molar mass of any compound.
Why grams to moles and moles to grams are both useful
Students and lab users rarely stay in one direction for long. A `grams to moles converter` is useful when you start with a weighed sample and need the amount of substance for stoichiometry. A `moles to grams converter` is useful when you know the target mole quantity and need to weigh out the right mass of reagent.
That is why this page supports both directions. The chemistry is the same relationship seen from opposite sides: divide by molar mass to go from grams to moles, and multiply by molar mass to go from moles to grams.
Worked example: water and carbon dioxide
Water has a molar mass of about 18.015 g/mol. That means 18.015 g of water is about 1 mol, while 2 mol of water weighs about 36.03 g. Carbon dioxide has a molar mass of about 44.01 g/mol, so 44.01 g corresponds to about 1 mol of CO2.
These examples matter because they show the pattern clearly: the mass in grams changes from substance to substance, but the mole relationship always depends on dividing or multiplying by that substance's molar mass.
The 1 mmol = mg shortcut
One of the most useful practical chemistry shortcuts is that the mass of 1 mmol in milligrams is numerically equal to the molar mass in g/mol. If a compound has a molar mass of 58.44 g/mol, then 1 mmol weighs 58.44 mg. If the molar mass is 180.156 g/mol, then 1 mmol weighs 180.156 mg.
This is not a separate formula. It falls directly out of the unit conversion between moles and millimoles, and between grams and milligrams. A better grams-to-moles calculator should make that shortcut visible because it comes up constantly in bench chemistry and solution prep.
Where this converter helps and where it does not
This converter is useful for stoichiometry setup, reagent weighing, simple lab prep, and homework checks where the molar mass is already known or can be found separately. It is especially helpful when you want to move from a formula's molar mass into a specific sample mass or mole amount without doing the arithmetic repeatedly by hand.
It does not calculate molar mass from a chemical formula by itself, balance chemical equations, determine limiting reagents, or prepare solutions from concentration and volume. For those jobs, use a molecular weight calculator, stoichiometry workflow, or molarity calculator as appropriate.
Frequently asked questions
How do I convert grams to moles without a calculator?
Divide the mass in grams by the molar mass. For example, 44 g of CO2 (molar mass 44.01 g/mol) is 44 / 44.01 ≈ 1.0 mol.
How do I convert moles to grams?
Multiply the mole quantity by the molar mass. For example, 2 mol of water at 18.015 g/mol weighs about 36.03 g.
What is the difference between moles and molecules?
A mole is a counting unit equal to 6.022 × 10²³ particles. One mole of water contains 6.022 × 10²³ water molecules, just as one dozen contains 12 items.
What molar mass do I use for a compound?
Use the compound's molecular weight expressed in g/mol. For a compound, that means summing the atomic weights of all atoms in the formula. If you do not already know the molar mass, calculate it first from the formula.
Why does 1 mmol have the same number in mg as g/mol?
Because 1 mmol is one-thousandth of a mole and 1 mg is one-thousandth of a gram. A compound with molar mass 58.44 g/mol therefore weighs 58.44 mg at 1 mmol.
Can I use this for stoichiometry?
Yes, for the mass-to-moles and moles-to-mass step. You still need the balanced equation and mole ratios separately if the question involves a reaction.
Does this page calculate molar mass from a formula?
No. This page assumes the molar mass is already known. If you only have the formula, calculate the molar mass first and then return here for the grams-to-moles conversion.
