Laboratory results for serum creatinine are reported in mg/dL in some countries and mmol/L in others, and the conversion runs through the molar mass: mmol/L = mg/dL × 10 ÷ 113.12, which for creatinine is a factor of 0.0884017. A reference interval of 0.6–1.2 mg/dL is therefore 0.05304–0.1061 mmol/L, the same interval in different clothes.
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 factor is specific to the substance being measured, which is why a single "divide by 18" cannot be applied across a report: that figure belongs to glucose alone. For creatinine the divisor is 11.312, and using the wrong one produces a number that looks plausible and is wrong by a factor of two or three — the commonest error in reading a foreign result.
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
mg/dL- The reported result in milligrams per decilitre
113.12- The molar mass of creatinine in g/mol, derived from its formula
mmol/L- The same result in millimoles per litre
How it works, step by step
- Enter the result as reported, in mg/dL.
- It is multiplied by 10 to give mg/L.
- That is divided by 113.12 g/mol to give mmol/L.
- The reference interval is shown in both units so the converted figure can be read against it.
Worked examples
0.6 mg/dL of serum creatinine in mmol/L
0.6 × 0.0884017 = 0.053041 mmol/L, which is 53.041 µmol/L. That result is at the bottom of the quoted interval of 0.6–1.2 mg/dL, or 0.05304–0.1061 mmol/L in the other unit.
0.9 mg/dL of serum creatinine in mmol/L
0.9 × 0.0884017 = 0.079562 mmol/L, which is 79.562 µmol/L. That result is in the middle of the quoted interval of 0.6–1.2 mg/dL, or 0.05304–0.1061 mmol/L in the other unit.
1.7 mg/dL of serum creatinine in mmol/L
1.7 × 0.0884017 = 0.15028 mmol/L, which is 150.28 µmol/L. That result is above the quoted interval of 0.6–1.2 mg/dL, or 0.05304–0.1061 mmol/L in the other unit.
How to read your score
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 do I convert serum creatinine from mg/dL to mmol/L?
Multiply by 10 and divide by the molar mass, 113.12 g/mol — a single factor of 0.0884017 for creatinine. To go back the other way, multiply the mmol/L figure by 11.312.
What is the reference range for serum creatinine in both units?
Taking 0.6–1.2 mg/dL as the interval (adult, varies with muscle mass), that is 0.05304–0.1061 mmol/L. Every laboratory publishes its own interval and the one printed on the report is the one that applies.
Why can I not use one conversion factor for the whole report?
Because the factor is the molar mass, and that differs for every analyte. For creatinine it is 0.0884017; a factor borrowed from another test gives a result that looks reasonable and is wrong by whatever ratio separates the two molar masses.
What about mg/L and µmol/L?
A decilitre is 100 mL, so mg/dL × 10 is mg/L: 0.6 mg/dL is 6 mg/L. Micromoles are millimoles × 1000, so the same result is 53.041 µmol/L. Reports for trace analytes use µmol/L to avoid decimals.
Unit conversion table for 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.
| mg/dL | mmol/L | µmol/L | mg/L | Against reference |
|---|---|---|---|---|
| 0.3 mg/dL | 0.026521 | 26.521 | 3 | below range |
| 0.42462 mg/dL | 0.037537 | 37.537 | 4.2462 | below range |
| 0.54923 mg/dL | 0.048553 | 48.553 | 5.4923 | below range |
| 0.67385 mg/dL | 0.059569 | 59.569 | 6.7385 | within range |
| 0.79846 mg/dL | 0.070585 | 70.585 | 7.9846 | within range |
| 0.92308 mg/dL | 0.081602 | 81.602 | 9.2308 | within range |
| 1.0477 mg/dL | 0.092618 | 92.618 | 10.477 | within range |
| 1.1723 mg/dL | 0.10363 | 103.63 | 11.723 | within range |
| 1.2969 mg/dL | 0.11465 | 114.65 | 12.969 | above range |
| 1.4215 mg/dL | 0.12567 | 125.67 | 14.215 | above range |
| 1.5462 mg/dL | 0.13668 | 136.68 | 15.462 | above range |
| 1.6708 mg/dL | 0.1477 | 147.7 | 16.708 | above range |
| 1.7954 mg/dL | 0.15872 | 158.72 | 17.954 | above range |
| 1.92 mg/dL | 0.16973 | 169.73 | 19.2 | above range |
Conversion factor mg/dL × 10 ÷ 113.12 = mmol/L. Reference interval taken as 0.6–1.2 mg/dL (adult, varies with muscle mass); laboratories publish their own intervals and those are the ones that apply to a result.
| 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.