The molar mass of creatinine, C4H7N3O, is 113.12 g/mol. That single number is what connects a mass you can weigh to an amount of substance you can react: one mole is 113.12 g, and a gram of it is 5.324e+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. Creatinine is 4 × 12.011 (C) + 7 × 1.008 (H) + 3 × 14.007 (N) + 15.999 (O), which is 113.12 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: 4 of the 15 atoms in a formula unit are carbon, and they account for 48.044 g of the 113.12 g, or 42.47% 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 creatinine is 113.12 mg and one micromole is 113.12 µg, so a balance reading to a milligram places you within 8.84 µmol. A single formula unit weighs 1.8784e-22 g, which is why the count in the gauge runs into the sextillions for any mass you can see.
The muscle breakdown product used to estimate kidney function. Reported in mg/dL or micromoles per litre, and the two scales differ by a factor of 88.4. At 113.12 g/mol it is heavier than 10 of the 21 organic compounds covered here, and that ranking matters more than it looks: toluene has a molar mass of 92.141 g/mol, so a gram of it contains 22.8% more formula units than a gram of creatinine. 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, 2.2624 g of every 113.12 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 creatinine in grams
113.12- The molar mass of creatinine 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 creatinine in grams.
- It is divided by the molar mass, 113.12 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 creatinine as a molecule count
0.5 g divided by 113.12 g/mol is 0.00442008 mol, and multiplying by the Avogadro constant gives 2.662e+21 formula units of creatinine. The same mass is 4.4201 mmol, which is the figure a reaction is actually planned in.
5 g of creatinine as a molecule count
5 g divided by 113.12 g/mol is 0.0442008 mol, and multiplying by the Avogadro constant gives 2.662e+22 formula units of creatinine. The same mass is 44.201 mmol, which is the figure a reaction is actually planned in.
50 g of creatinine as a molecule count
50 g divided by 113.12 g/mol is 0.442008 mol, and multiplying by the Avogadro constant gives 2.662e+23 formula units of creatinine. The same mass is 442.01 mmol, which is the figure a reaction is actually planned in.
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Frequently asked questions
What is the molar mass of creatinine (C4H7N3O)?
It is 113.12 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 4 × 12.011 (C) + 7 × 1.008 (H) + 3 × 14.007 (N) + 15.999 (O). One mole of creatinine therefore weighs 113.12 g, and a gram of it is 8.8402 mmol.
What percentage of creatinine is carbon?
42.47% by mass. Each formula unit contains 4 carbon atoms contributing 48.044 g of the 113.12 g total, so 100 g of creatinine contains 42.47 g of carbon and a kilogram contains 424.72 g of it.
How many molecules are in one gram of creatinine?
About 5.324e+21. One gram is 0.00884017 mol, and each mole contains 6.02214076 × 10²³ formula units by definition of the mole, so the count is that constant divided by 113.12.
How much does a single molecule of creatinine weigh?
1.8784e-22 g, which is 113.12 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 creatinine it is 113.12. Molar mass carries grams per mole: 113.12 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 creatinine comes out at 113.12 g/mol rather than 113.
Molar mass, composition and mole equivalents of creatinine
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Carbon (C) | 4 | 12.011 | 48.044 | 42.47% |
| Nitrogen (N) | 3 | 14.007 | 42.021 | 37.15% |
| Oxygen (O) | 1 | 15.999 | 15.999 | 14.14% |
| Hydrogen (H) | 7 | 1.008 | 7.056 | 6.238% |
| Total — one mole of creatinine | 113.12 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 113.12 g/mol.
| Amount | Mass (g) | Mass (mg) | Formula units |
|---|---|---|---|
| 1 µmol | 0.00011312 | 0.11312 | 6.022e+17 |
| 10 µmol | 0.0011312 | 1.1312 | 6.022e+18 |
| 100 µmol | 0.011312 | 11.312 | 6.022e+19 |
| 1 mmol | 0.11312 | 113.12 | 6.022e+20 |
| 10 mmol | 1.1312 | 1131.2 | 6.022e+21 |
| 50 mmol | 5.656 | 5656 | 3.011e+22 |
| 100 mmol | 11.312 | 11,312 | 6.022e+22 |
| 250 mmol | 28.28 | 28,280 | 1.506e+23 |
| 500 mmol | 56.56 | 56,560 | 3.011e+23 |
| 750 mmol | 84.84 | 84,840 | 4.517e+23 |
| 1 mol | 113.12 | 113,120 | 6.022e+23 |
| 2 mol | 226.24 | 226,240 | 1.204e+24 |
| 5 mol | 565.6 | 565,600 | 3.011e+24 |
| 10 mol | 1131.2 | 1131200.000000 | 6.022e+24 |
Mass is the amount multiplied by 113.12 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 |
|---|---|---|---|
| Benzene | C6H6 | 78.114 | 12.802 |
| Glycerol | C3H8O3 | 92.094 | 10.858 |
| Toluene | C7H8 | 92.141 | 10.853 |
| Creatinine (this page) | C4H7N3O | 113.12 | 8.8402 |
| Octane | C8H18 | 114.232 | 8.7541 |
| Tris base | C4H11NO3 | 121.136 | 8.2552 |
| Paracetamol | C8H9NO2 | 151.165 | 6.6153 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.