The molar mass of uric acid, C5H4N4O3, is 168.112 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 168.112 g, and a gram of it is 3.582e+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. Uric acid is 5 × 12.011 (C) + 4 × 1.008 (H) + 4 × 14.007 (N) + 3 × 15.999 (O), which is 168.112 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Carbon makes up the largest share of the mass: 5 of the 16 atoms in a formula unit are carbon, and they account for 60.055 g of the 168.112 g, or 35.72% 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 uric acid is 168.112 mg and one micromole is 168.112 µg, so a balance reading to a milligram places you within 5.948 µmol. A single formula unit weighs 2.7916e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
The end point of purine metabolism and the crystal that causes gout. Barely soluble in water, which is precisely why it crystallises in joints. At 168.112 g/mol it is heavier than 14 of the 21 organic compounds covered here, and that ranking matters more than it looks: paracetamol has a molar mass of 151.165 g/mol, so a gram of it contains 11.2% more formula units than a gram of uric acid. Weigh by mass and you are not weighing equal amounts of substance.
Purity is the usual gap between the calculation and the balance. A reagent sold at 98% means 3.3622 g of a nominal 168.112 g is something else, so for exact work you divide the weighed mass by the assay figure on the certificate. For most purposes the difference is smaller than the error in reading the meniscus, but it is systematic rather than random, so it does not average out.
The formula
m- The mass of uric acid in grams
168.112- The molar mass of uric 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 uric acid in grams.
- It is divided by the molar mass, 168.112 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 uric acid as a molecule count
0.5 g divided by 168.112 g/mol is 0.00297421 mol, and multiplying by the Avogadro constant gives 1.791e+21 formula units of uric acid. The same mass is 2.9742 mmol, which is the figure a reaction is actually planned in.
5 g of uric acid as a molecule count
5 g divided by 168.112 g/mol is 0.0297421 mol, and multiplying by the Avogadro constant gives 1.791e+22 formula units of uric acid. The same mass is 29.742 mmol, which is the figure a reaction is actually planned in.
50 g of uric acid as a molecule count
50 g divided by 168.112 g/mol is 0.297421 mol, and multiplying by the Avogadro constant gives 1.791e+23 formula units of uric acid. The same mass is 297.42 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 uric acid (C5H4N4O3)?
It is 168.112 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 5 × 12.011 (C) + 4 × 1.008 (H) + 4 × 14.007 (N) + 3 × 15.999 (O). One mole of uric acid therefore weighs 168.112 g, and a gram of it is 5.9484 mmol.
What percentage of uric acid is carbon?
35.72% by mass. Each formula unit contains 5 carbon atoms contributing 60.055 g of the 168.112 g total, so 100 g of uric acid contains 35.72 g of carbon and a kilogram contains 357.23 g of it.
How many molecules are in one gram of uric acid?
About 3.582e+21. One gram is 0.00594842 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 168.112.
How much does a single molecule of uric acid weigh?
2.7916e-22 g, which is 168.112 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 uric acid it is 168.112. Molar mass carries grams per mole: 168.112 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. Carbon is quoted as 12.011 rather than a whole number for that reason, and the same applies to the other elements here, which is why uric acid comes out at 168.112 g/mol rather than 168.
Molar mass, composition and mole equivalents of uric acid
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 5 | 12.011 | 60.055 | 35.72% |
| Nitrogen (N) | 4 | 14.007 | 56.028 | 33.33% |
| Oxygen (O) | 3 | 15.999 | 47.997 | 28.55% |
| Hydrogen (H) | 4 | 1.008 | 4.032 | 2.398% |
| Total — one mole of uric acid | 168.112 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 168.112 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000168112 | 0.168112 | 6.022e+17 |
| 10 µmol | 0.00168112 | 1.68112 | 6.022e+18 |
| 100 µmol | 0.0168112 | 16.8112 | 6.022e+19 |
| 1 mmol | 0.168112 | 168.112 | 6.022e+20 |
| 10 mmol | 1.68112 | 1681.12 | 6.022e+21 |
| 50 mmol | 8.4056 | 8405.6 | 3.011e+22 |
| 100 mmol | 16.8112 | 16,811.2 | 6.022e+22 |
| 250 mmol | 42.028 | 42,028 | 1.506e+23 |
| 500 mmol | 84.056 | 84,056 | 3.011e+23 |
| 750 mmol | 126.084 | 126,084 | 4.517e+23 |
| 1 mol | 168.112 | 168,112 | 6.022e+23 |
| 2 mol | 336.224 | 336,224 | 1.204e+24 |
| 5 mol | 840.56 | 840,560 | 3.011e+24 |
| 10 mol | 1681.12 | 1681120.000000 | 6.022e+24 |
Mass is the amount multiplied by 168.112 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 |
|---|---|---|---|
| Octane | C8H18 | 114.232 | 8.7541 |
| Tris base | C4H11NO3 | 121.136 | 8.2552 |
| Paracetamol | C8H9NO2 | 151.165 | 6.6153 |
| Uric acid (this page) | C5H4N4O3 | 168.112 | 5.9484 |
| Glucose | C6H12O6 | 180.156 | 5.5507 |
| Aspirin | C9H8O4 | 180.159 | 5.5507 |
| Caffeine | C8H10N4O2 | 194.194 | 5.1495 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.