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Short answer: The molecular weight of urea (CH4N2O, CAS 57-13-6) is 60.0553 g/mol according to the NIST Chemistry WebBook. Urea is very soluble in water (545 g/L at 25 °C per PubChem), which is why it is a standard chaotropic reagent for denaturing protein buffers. This page gives the number, the arithmetic for making a molar stock, and the solution-stability rules that bench protocols attach to it. It is general reagent information for research use, not medical advice.
Definition and scope
What is the definition of urea?
Urea is a small organic compound with the formula CH4N2O, written structurally as (NH2)2CO. NIST lists it under the alternative names carbamide and carbonyldiamide, and the German name Harnstoff. Its identifiers are CAS Registry Number 57-13-6 and InChIKey XSQUKJJJFZCRTK-UHFFFAOYSA-N.
What is the chemical name of urea?
The everyday name is urea; the common synonym is carbamide. Catalogue and database records use the CAS number 57-13-6 to remove any ambiguity between synonyms.
Urea molecular weight and the numbers a protocol needs
NIST gives a molecular weight of 60.0553 for CH4N2O. In molar terms that is 60.0553 g/mol, and the figures below are simple arithmetic from it (calculated here, not quoted from a vendor).
| Target concentration | Mass of urea per litre of final solution | Basis |
|---|---|---|
| 1 M | 60.06 g | calculated: 1 mol x 60.0553 g/mol |
| 6 M | 360.33 g | calculated |
| 8 M | 480.44 g | calculated |
| 8.5 M | 510.47 g | calculated; 8.5 M is the stock concentration Bio-Rad describes for IEF sample preparation |
Because dissolving this much urea increases the volume of the solution, weigh the urea, dissolve it in less water than the target, and then bring the solution up to the final volume rather than adding the full volume of water to the solid. For general molarity conversions see the CASRAI guides on moles to molarity and molarity to millimoles.
Urea solubility
Solubility is reported by different sources in different ways, so each row below carries its own source.
| Solvent | Reported solubility | Source |
|---|---|---|
| Water | 545,000 mg/L (545 g/L) at 25 °C | PubChem, citing Yalkowsky (1989) |
| Water | Miscible | PubChem, citing ICSC 0595 |
| Ethanol | Soluble | PubChem, citing the EU food-additive specification |
| Benzene | Insoluble | PubChem, citing CRC |
| Chloroform, ether | Almost insoluble | PubChem, citing the Merck Index |
The PubChem solubility record read for this page does not give a DMSO figure, so none is stated here; take DMSO values from the product information sheet of the lot you are using.
Is urea a polar or nonpolar molecule?
Urea behaves as a polar compound: its very high solubility in water and ethanol and its insolubility in benzene, as listed above, are the pattern expected of a polar solute.
Urea stock solution and storage temperature
The practical issue with urea at the bench is not dissolving it but keeping the solution chemically clean. Bio-Rad Bulletin 6220 (IEF sample preparation) gives the following guidance.
- Cyanate formation. Urea in solution exists in equilibrium with ammonium cyanate, which can cause irreversible protein modification (carbamylation).
- Freshness or clean-up. Use stock solutions soon after they are made, or treat them with a mixed-bed ion exchange resin to avoid carbamylation by cyanate that forms in old urea.
- Storage temperature. For a deionized 8.5 M stock, store convenient aliquots at -20 °C, and do not store urea solutions at room temperature or 4 °C any longer than necessary.
- Heating. Urea should not be heated above 30 °C, because carbamylation of the sample may occur.
- Purity. High-purity urea should be used for IEF.
For how urea is used once the stock is made, see the CASRAI guides on protein refolding and isoelectric focusing.
Where it matters for labs
Using the molecular weight correctly decides whether a denaturing buffer is the concentration the protocol intends, and the stability guidance decides whether the urea stays inert toward the protein. A checklist drawn from the sources above: calculate mass from 60.0553 g/mol, bring to final volume, use high-purity urea, prepare fresh or deionize, keep below the protocol’s stated temperature, and freeze aliquots rather than leaving the solution on the bench.
Common misunderstandings
What is the weight of urea fertilizer?
Molecular weight is a property of the molecule (60.0553 g/mol), not of a bag of fertilizer; a bag weight is a packaging quantity set by the seller. The chemical figure that matters for fertilizer is nitrogen content: two nitrogen atoms (2 x 14.007 = 28.014) over 60.0553 gives about 46.6 percent nitrogen by mass. This percentage is calculated from atomic masses, not quoted from a fertilizer specification. Urea also appears in instant cold pack ingredients, where it is likewise just a chemical, not defined by any package weight.
Other points
- Molecular weight and molar mass are used interchangeably at the bench; both are 60.06 g/mol here.
- An old urea solution is not equivalent to a fresh one at the same nominal concentration, because of the cyanate equilibrium described above.
FAQ
What is the molecular weight of urea?
60.0553 g/mol (NIST Chemistry WebBook, formula CH4N2O).
How much urea makes 1 L of 8 M solution?
Calculated: 480.44 g, brought to a final volume of 1 L.
How should urea stock solutions be stored?
Per Bio-Rad Bulletin 6220, as frozen aliquots at -20 °C for a deionized 8.5 M stock; avoid prolonged storage at room temperature or 4 °C.
What is the chemical name of urea?
Urea, also called carbamide (CAS 57-13-6).
Sources
- NIST Chemistry WebBook, Urea (CAS 57-13-6), webbook.nist.gov/cgi/cbook.cgi?ID=C57136, read 2026-11-07.
- PubChem compound record for urea, solubility section, pubchem.ncbi.nlm.nih.gov/compound/1176, read 2026-11-07.
- Bio-Rad Bulletin 6220, bio-rad.com/webroot/web/pdf/lsr/literature/Bulletin_6220.pdf, read 2026-11-07.
