The molar mass of nitric acid, HNO3, is 63.012 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 63.012 g, and a gram of it is 9.557e+21 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. Nitric acid is 1.008 (H) + 14.007 (N) + 3 × 15.999 (O), which is 63.012 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 3 of the 5 atoms in a formula unit are oxygen, and they account for 47.997 g of the 63.012 g, or 76.17% 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 nitric acid is 63.012 mg and one micromole is 63.012 µg, so a balance reading to a milligram places you within 15.87 µmol. A single formula unit weighs 1.0463e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
The acid for nitration and metal digestion. Concentrated is 68% w/w, near 15.8 mol/L, and it stains skin yellow on contact. At 63.012 g/mol it is heavier than 4 of the 12 acids covered here, and that ranking matters more than it looks: boric acid has a molar mass of 61.831 g/mol, so a gram of it contains 1.91% more formula units than a gram of nitric acid. Weigh by mass and you are not weighing equal amounts of substance.
One more step applies if you are starting from a concentrated bottle. Concentrated acids are labelled as a percentage by weight together with a density, not as a molarity, so getting to mol/L means multiplying density by that percentage and dividing by 63.012 g/mol. A page like this one gives you the last of those three numbers; the first two are on the bottle, and they vary between grades.
The formula
m- The mass of nitric acid in grams
63.012- The molar mass of nitric acid 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 nitric acid in grams.
- It is divided by the molar mass, 63.012 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 nitric acid as a molecule count
0.5 g divided by 63.012 g/mol is 0.007935 mol, and multiplying by the Avogadro constant gives 4.779e+21 formula units of nitric acid. The same mass is 7.935 mmol, which is the figure a reaction is actually planned in.
5 g of nitric acid as a molecule count
5 g divided by 63.012 g/mol is 0.07935 mol, and multiplying by the Avogadro constant gives 4.779e+22 formula units of nitric acid. The same mass is 79.35 mmol, which is the figure a reaction is actually planned in.
50 g of nitric acid as a molecule count
50 g divided by 63.012 g/mol is 0.7935 mol, and multiplying by the Avogadro constant gives 4.779e+23 formula units of nitric acid. The same mass is 793.5 mmol, which is the figure a reaction is actually planned in.
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Frequently asked questions
What is the molar mass of nitric acid (HNO3)?
It is 63.012 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 1.008 (H) + 14.007 (N) + 3 × 15.999 (O). One mole of nitric acid therefore weighs 63.012 g, and a gram of it is 15.87 mmol.
What percentage of nitric acid is oxygen?
76.17% by mass. Each formula unit contains 3 oxygen atoms contributing 47.997 g of the 63.012 g total, so 100 g of nitric acid contains 76.17 g of oxygen and a kilogram contains 761.71 g of it.
How many molecules are in one gram of nitric acid?
About 9.557e+21. One gram is 0.01587 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 63.012.
How much does a single molecule of nitric acid weigh?
1.0463e-22 g, which is 63.012 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 nitric acid it is 63.012. Molar mass carries grams per mole: 63.012 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. Oxygen is quoted as 15.999 rather than a whole number for that reason, and the same applies to the other elements here, which is why nitric acid comes out at 63.012 g/mol rather than 63.
Molar mass, composition and mole equivalents of nitric acid
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 3 | 15.999 | 47.997 | 76.17% |
| Nitrogen (N) | 1 | 14.007 | 14.007 | 22.23% |
| Hydrogen (H) | 1 | 1.008 | 1.008 | 1.6% |
| Total — one mole of nitric acid | 63.012 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 63.012 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000063 | 0.063012 | 6.022e+17 |
| 10 µmol | 0.00063012 | 0.63012 | 6.022e+18 |
| 100 µmol | 0.0063012 | 6.3012 | 6.022e+19 |
| 1 mmol | 0.063012 | 63.012 | 6.022e+20 |
| 10 mmol | 0.63012 | 630.12 | 6.022e+21 |
| 50 mmol | 3.1506 | 3150.6 | 3.011e+22 |
| 100 mmol | 6.3012 | 6301.2 | 6.022e+22 |
| 250 mmol | 15.753 | 15,753 | 1.506e+23 |
| 500 mmol | 31.506 | 31,506 | 3.011e+23 |
| 750 mmol | 47.259 | 47,259 | 4.517e+23 |
| 1 mol | 63.012 | 63,012 | 6.022e+23 |
| 2 mol | 126.024 | 126,024 | 1.204e+24 |
| 5 mol | 315.06 | 315,060 | 3.011e+24 |
| 10 mol | 630.12 | 630,120 | 6.022e+24 |
Mass is the amount multiplied by 63.012 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 |
|---|---|---|---|
| Formic acid | CH2O2 | 46.025 | 21.727 |
| Acetic acid | CH3COOH | 60.052 | 16.652 |
| Boric acid | H3BO3 | 61.831 | 16.173 |
| Nitric acid (this page) | HNO3 | 63.012 | 15.87 |
| Oxalic acid | C2H2O4 | 90.034 | 11.107 |
| Lactic acid | C3H6O3 | 90.078 | 11.101 |
| Phosphoric acid | H3PO4 | 97.99376 | 10.205 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.