Grams to Moles Calculator

A gram counts mass, a mole counts particles

A kitchen scale answers one question: how much stuff is there, by weight. A mole answers a different one: how many particles are in it. That is why 5 grams of salt and 5 grams of sugar weigh the same but behave nothing alike, and why chemists stop using grams the moment a reaction has to balance.

One mole is exactly 6.02214076 x 10^23 particles. That number, the Avogadro constant, stopped being a measured quirk in 2019 and became a fixed definition of the mole, as NIST describes in its mole redefinition page. It is a count, the way a dozen is a count, only large enough that the particles in a spoonful come out in whole numbers.

Grams and moles meet through molar mass, which is the weight of one mole of a substance. Water is 18.02 grams per mole, salt is 58.44, sugar is 342.30. Those three numbers are the whole bridge between the scale and the particle count, and every conversion on this page is built from them.

The formula: grams divided by molar mass

One division takes you from mass to moles:

• Moles = grams / molar mass
• Grams = moles x molar mass

The units do the explaining. Molar mass is grams per mole, so grams divided by grams per mole leaves moles, and moles multiplied by grams per mole leaves grams. Two worked runs with kitchen numbers:

• 5 / 58.44 = 0.0856 mol of table salt in a 5 gram pinch
• 0.25 x 192.12 = 48.03 grams of citric acid in a quarter mole

A water bottle makes the scale concrete. Five hundred milliliters of water weighs about 500 grams, and 500 / 18.02 = 27.75 moles, which is 1.67 x 10^25 molecules in a bottle you can hold in one hand.

Two words get mixed up here. Molar mass is a mass per mole, reported in grams per mole. Molecular mass is the mass of one molecule, reported in daltons or atomic mass units. The number is the same, the unit is not, and salt has no molecules at all: it is a lattice of ions, so the correct term is formula unit. The mole count is still right, which is what matters for a recipe or a brine.

Molar masses for twelve kitchen chemicals

These values are built from the standard atomic weights published by the Commission on Isotopic Abundances and Atomic Weights, using hydrogen 1.008, carbon 12.011, nitrogen 14.007, oxygen 15.999, sodium 22.990, chlorine 35.45, potassium 39.098, calcium 40.078, sulfur 32.06 and magnesium 24.305. Salt, for example, is 22.990 + 35.45 = 58.44 grams per mole.

Hydrated salts carry water in the crystal. Epsom salt is MgSO4 with seven water molecules attached, so its molar mass includes 7 x 18.02 = 126.14 grams of water on top of the 120.33 grams of magnesium sulfate.

Worked example: 30 grams of salt in a brine

Brine recipes are written in weight percentages, which makes them a natural place to count moles. Thirty grams of salt in a kilogram of water is 30 + 1000 = 1030 grams of solution, a 2.91 percent brine by weight. In moles, 30 / 58.44 = 0.5133 mol of salt, dissolved in 1 kilogram of water, so the molality is 0.513 mol per kilogram.

If you measure the water by volume instead, 1 liter of water weighs 1 kilogram only near 4 degrees Celsius, and it weighs about 0.997 kilogram at room temperature. Close enough for pickling, not close enough for a lab. The volume of the finished brine also grows once the salt dissolves, so a 1 liter batch holds slightly less than a liter of water.

A 2 percent brine, the common starting point for pickles and poultry, is 20 grams of salt per kilogram of water, which is 20 / 58.44 = 0.3422 mol per kilogram. Nothing in the cooking changes with that number. What changes is that you can now compare two brines, or two acids, on the same footing instead of guessing from the scoop size.

Millimoles and particle counts for small doses

Half a teaspoon of baking soda is roughly 3 grams, and a rounded pinch is closer to 0.5 gram. Those small weights turn into small mole counts, so the working unit is the millimole, one thousandth of a mole.

• 3 / 84.01 = 0.0357 mol, so 35.71 millimoles of baking soda in 3 grams
• 0.5 / 84.01 = 0.005952 mol, so 5.95 millimoles in 500 milligrams

To count particles, multiply the moles by 6.02214076 x 10^23. Half a gram of baking soda gives 0.005952 x 6.02214076 x 10^23, which is 3.58 x 10^21 formula units. Written out that is 3,580,000,000,000,000,000,000 units, a number no kitchen needs but a chemistry problem usually does.

The same shift happens on supplement and medicine labels, which report milligrams of a mineral rather than the compound. 500 milligrams of calcium chloride is 0.5 / 110.98 = 0.00451 mol, but only 0.00451 mol of calcium, because each formula unit carries one calcium ion. Read the formula before you trust the mole count.

Same weight, different particle count

One hundred grams is one hundred grams on any scale, but the mole count behind it depends entirely on molar mass. The table below does the same division for five substances.

Salt delivers 5.86 times as many formula units as sugar at the same weight, because one salt unit weighs 58.44 and one sugar molecule weighs 342.30. This is the number that matters when you compare how much of an acid or a salt is in two recipes: grams hide the difference, moles show it.

Where moles help in a kitchen and where they mislead

Moles help when two chemicals have to meet in a fixed ratio. Baking soda and citric acid react one to one on the bicarbonate side, but citric acid brings three acidic protons, so one mole of citric acid neutralizes three moles of bicarbonate. Three grams of baking soda is 0.0357 mol, which needs 0.0119 mol of citric acid, or 0.0119 x 192.12 = 2.29 grams. That is the arithmetic behind a fizzy bath bomb or a sour candy, and it is the reason a recipe scaled by volume alone can taste flat or soapy.

Moles mislead when the ingredient is a mixture. Flour, milk and honey have no single molar mass, so a mole of flour is a meaningless phrase. Water is the exception that proves it: 18.02 is exact enough for water, but a cup of it still has to be weighed to know how many moles you poured.

Two related tools cover the neighbouring jobs. If you have a chemical formula and want its molar mass, the molar mass calculator reads the formula for you. If you are making a solution and want molarity, the molarity calculator takes mass, molar mass and volume together. This page is narrower on purpose: a substance you can pick from a list, a weight in grams, and the mole count that comes out.