The molar mass of urea, CH4N2O, is 60.056 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 60.056 g, and a gram of it is 1.003e+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. Urea is 12.011 (C) + 4 × 1.008 (H) + 2 × 14.007 (N) + 15.999 (O), which is 60.056 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Nitrogen makes up the largest share of the mass: 2 of the 8 atoms in a formula unit are nitrogen, and they account for 28.014 g of the 60.056 g, or 46.65% 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 urea is 60.056 mg and one micromole is 60.056 µg, so a balance reading to a milligram places you within 16.65 µmol. A single formula unit weighs 9.9725e-23 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
The nitrogen fertiliser with the highest nitrogen content, a skin humectant, and the compound the body uses to excrete nitrogen — reported as BUN. At 60.056 g/mol it is heavier than 3 of the 21 organic compounds covered here, and that ranking matters more than it looks: acetone has a molar mass of 58.08 g/mol, so a gram of it contains 3.4% more formula units than a gram of urea. 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, 1.2011 g of every 60.056 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 urea in grams
60.056- The molar mass of urea 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 urea in grams.
- It is divided by the molar mass, 60.056 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 urea as a molecule count
0.5 g divided by 60.056 g/mol is 0.00832556 mol, and multiplying by the Avogadro constant gives 5.014e+21 formula units of urea. The same mass is 8.3256 mmol, which is the figure a reaction is actually planned in.
5 g of urea as a molecule count
5 g divided by 60.056 g/mol is 0.0832556 mol, and multiplying by the Avogadro constant gives 5.014e+22 formula units of urea. The same mass is 83.256 mmol, which is the figure a reaction is actually planned in.
50 g of urea as a molecule count
50 g divided by 60.056 g/mol is 0.832556 mol, and multiplying by the Avogadro constant gives 5.014e+23 formula units of urea. The same mass is 832.56 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 urea (CH4N2O)?
It is 60.056 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 12.011 (C) + 4 × 1.008 (H) + 2 × 14.007 (N) + 15.999 (O). One mole of urea therefore weighs 60.056 g, and a gram of it is 16.651 mmol.
What percentage of urea is nitrogen?
46.65% by mass. Each formula unit contains 2 nitrogen atoms contributing 28.014 g of the 60.056 g total, so 100 g of urea contains 46.65 g of nitrogen and a kilogram contains 466.46 g of it.
How many molecules are in one gram of urea?
About 1.003e+22. One gram is 0.0166511 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 60.056.
How much does a single molecule of urea weigh?
9.9725e-23 g, which is 60.056 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 urea it is 60.056. Molar mass carries grams per mole: 60.056 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. Nitrogen is quoted as 14.007 rather than a whole number for that reason, and the same applies to the other elements here, which is why urea comes out at 60.056 g/mol rather than 60.
Molar mass, composition and mole equivalents of urea
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Nitrogen (N) | 2 | 14.007 | 28.014 | 46.65% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 26.64% |
| Carbon (C) | 1 | 12.011 | 12.011 | 20% |
| Hydrogen (H) | 4 | 1.008 | 4.032 | 6.714% |
| Total — one mole of urea | 60.056 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 60.056 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.000060 | 0.060056 | 6.022e+17 |
| 10 µmol | 0.00060056 | 0.60056 | 6.022e+18 |
| 100 µmol | 0.0060056 | 6.0056 | 6.022e+19 |
| 1 mmol | 0.060056 | 60.056 | 6.022e+20 |
| 10 mmol | 0.60056 | 600.56 | 6.022e+21 |
| 50 mmol | 3.0028 | 3002.8 | 3.011e+22 |
| 100 mmol | 6.0056 | 6005.6 | 6.022e+22 |
| 250 mmol | 15.014 | 15,014 | 1.506e+23 |
| 500 mmol | 30.028 | 30,028 | 3.011e+23 |
| 750 mmol | 45.042 | 45,042 | 4.517e+23 |
| 1 mol | 60.056 | 60,056 | 6.022e+23 |
| 2 mol | 120.112 | 120,112 | 1.204e+24 |
| 5 mol | 300.28 | 300,280 | 3.011e+24 |
| 10 mol | 600.56 | 600,560 | 6.022e+24 |
Mass is the amount multiplied by 60.056 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 |
|---|---|---|---|
| Methanol | CH4O | 32.042 | 31.209 |
| Ethanol | C2H6O | 46.069 | 21.707 |
| Acetone | C3H6O | 58.08 | 17.218 |
| Urea (this page) | CH4N2O | 60.056 | 16.651 |
| Isopropyl alcohol | C3H8O | 60.096 | 16.64 |
| Ethylene glycol | C2H6O2 | 62.068 | 16.111 |
| Glycine | C2H5NO2 | 75.067 | 13.321 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.