SMILES to Molecular Weight Calculator
In short: Paste a SMILES string and get molecular weight, formula, IUPAC name, and PubChem CID when available. It is free, works in your web browser and needs no download.
Paste a SMILES string to calculate molecular weight and retrieve the matching formula when PubChem has a compound record.
How SMILES Molecular Weight Lookup Works
The tool resolves the SMILES string through PubChem and reads the molecular weight property from the matched compound record.
- For formula-only workflows, use the molecular weight calculator.
- For mass spectrometry formula checks, use exact mass instead of average molecular weight.
Molecular weight versus exact mass
Molecular weight (molar mass) is calculated from standard atomic weights, which average over natural isotope abundances: about 12.011 for carbon, 1.008 for hydrogen, 15.999 for oxygen, and 14.007 for nitrogen. It is the value to use for weighing reagents and preparing solutions. Exact (monoisotopic) mass uses only the most abundant isotope of each element and is the value to compare with high-resolution mass spectra.
Worked example
Aspirin, CC(=O)OC1=CC=CC=C1C(=O)O, is C9H8O4.
9 × 12.011 + 8 × 1.008 + 4 × 15.999 = 108.099 + 8.064 + 63.996 = 180.16 g/mol. Its monoisotopic mass is about 180.042 Da.
Practical uses
- To make 100 mL of a 0.1 M solution, you need 0.01 mol, which is 1.80 g of aspirin.
- For hydrates and salts, include the counter-ion and water in the SMILES so the weight matches the bottle you are weighing from.
Continue with the Grams to Moles or Solution Prep calculators.
Last updated: