The molar mass of sodium chloride, NaCl, is 58.439769 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 58.43977 g, and a gram of it is 1.03e+22 formula units. The calculator turns any weighed mass into that count, and reports the amount in moles, millimoles and the mass of a single formula unit alongside it.
The figure comes from the formula. Sodium chloride is 22.9898 (Na) + 35.45 (Cl), which is 58.439769 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Chlorine makes up the largest share of the mass: 1 of the 2 atoms in a formula unit is chlorine, and they account for 35.45 g of the 58.43977 g, or 60.66% by mass. The derivation table below breaks the whole molecule down element by element.
The numbers a bench actually uses sit at the millimole scale. One millimole of sodium chloride is 58.4398 mg and one micromole is 58.4398 µg, so a balance reading to a milligram places you within 17.11 µmol. A single formula unit weighs 9.7042e-23 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
Table salt, and the solute in saline. A 0.9% w/v solution is isotonic with blood, which is the one concentration worth memorising. At 58.43977 g/mol it is heavier than 1 of the 34 salts covered here, and that ranking matters more than it looks: ammonium chloride has a molar mass of 53.489 g/mol, so a gram of it contains 9.26% more formula units than a gram of sodium chloride. Weigh by mass and you are not weighing equal amounts of substance.
Two practical things move the result. Purity below 100% means the weighed mass overstates how much compound you have — at 98% assay, 1.1688 g of every 58.43977 g is not the compound — and any water picked up from the air does the same. Both are systematic, so they shift every solution made from that jar in the same direction.
The formula
m- The mass of sodium chloride in grams
58.439769- The molar mass of sodium chloride in g/mol, derived from its formula
N- The number of formula units that mass contains
How it works, step by step
- Enter a mass of sodium chloride in grams.
- It is divided by the molar mass, 58.439769 g/mol, giving the amount in moles.
- That amount is multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole, to give the number of formula units.
- The panel also reports the amount in moles and millimoles and the mass of one formula unit.
Worked examples
0.5 g of sodium chloride as a molecule count
0.5 g divided by 58.43977 g/mol is 0.00855582 mol, and multiplying by the Avogadro constant gives 5.152e+21 formula units of sodium chloride. The same mass is 8.5558 mmol, which is the figure a reaction is actually planned in.
5 g of sodium chloride as a molecule count
5 g divided by 58.43977 g/mol is 0.0855582 mol, and multiplying by the Avogadro constant gives 5.152e+22 formula units of sodium chloride. The same mass is 85.558 mmol, which is the figure a reaction is actually planned in.
50 g of sodium chloride as a molecule count
50 g divided by 58.43977 g/mol is 0.855582 mol, and multiplying by the Avogadro constant gives 5.152e+23 formula units of sodium chloride. The same mass is 855.58 mmol, which is the figure a reaction is actually planned in.
How to read your score
Frequently asked questions
What is the molar mass of sodium chloride (NaCl)?
It is 58.439769 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 22.9898 (Na) + 35.45 (Cl). One mole of sodium chloride therefore weighs 58.43977 g, and a gram of it is 17.112 mmol.
What percentage of sodium chloride is chlorine?
60.66% by mass. Each formula unit contains 1 chlorine atom contributing 35.45 g of the 58.43977 g total, so 100 g of sodium chloride contains 60.66 g of chlorine and a kilogram contains 606.61 g of it.
How many molecules are in one gram of sodium chloride?
About 1.03e+22. One gram is 0.0171116 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 58.43977.
How much does a single molecule of sodium chloride weigh?
9.7042e-23 g, which is 58.439769 daltons. It is the molar mass divided by the Avogadro constant, and the number in daltons is numerically the same as the molar mass in g/mol — that equivalence is what makes the mole convenient.
Is molar mass the same as molecular weight?
They are the same number in ordinary use but not the same quantity. Molecular weight, properly relative molecular mass, is a ratio and has no unit: for sodium chloride it is 58.439769. Molar mass carries grams per mole: 58.439769 g/mol. Because the mole is defined so those agree, you can read one off the other.
Why is the molar mass not a whole number?
Because standard atomic weights are averages over the isotopes found in nature. Chlorine is quoted as 35.45 rather than a whole number for that reason, and the same applies to the other elements here, which is why sodium chloride comes out at 58.439769 g/mol rather than 58.
Molar mass, composition and mole equivalents of sodium chloride
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Chlorine (Cl) | 1 | 35.45 | 35.45 | 60.66% |
| Sodium (Na) | 1 | 22.98977 | 22.98977 | 39.34% |
| Total — one mole of sodium chloride | 58.439769 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 58.439769 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000058 | 0.0584398 | 6.022e+17 |
| 10 µmol | 0.000584398 | 0.584398 | 6.022e+18 |
| 100 µmol | 0.00584398 | 5.84398 | 6.022e+19 |
| 1 mmol | 0.0584398 | 58.4398 | 6.022e+20 |
| 10 mmol | 0.584398 | 584.398 | 6.022e+21 |
| 50 mmol | 2.92199 | 2921.99 | 3.011e+22 |
| 100 mmol | 5.84398 | 5843.98 | 6.022e+22 |
| 250 mmol | 14.6099 | 14,609.9 | 1.506e+23 |
| 500 mmol | 29.2199 | 29,219.9 | 3.011e+23 |
| 750 mmol | 43.8298 | 43,829.8 | 4.517e+23 |
| 1 mol | 58.4398 | 58,439.8 | 6.022e+23 |
| 2 mol | 116.88 | 116,880 | 1.204e+24 |
| 5 mol | 292.199 | 292,199 | 3.011e+24 |
| 10 mol | 584.398 | 584,398 | 6.022e+24 |
Mass is the amount multiplied by 58.439769 g/mol. The last column is that amount multiplied by the Avogadro constant, 6.02214076 × 10²³ per mole.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Ammonium chloride | NH4Cl | 53.489 | 18.695 |
| Sodium chloride (this page) | NaCl | 58.43977 | 17.112 |
| Sodium nitrite | NaNO2 | 68.99477 | 14.494 |
| Sodium hypochlorite | NaClO | 74.43877 | 13.434 |
| Potassium chloride | KCl | 74.5483 | 13.414 |
| Ammonium nitrate | NH4NO3 | 80.043 | 12.493 |
| Sodium bicarbonate | NaHCO3 | 84.00577 | 11.904 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.