Molecular Weight Calculator
Enter a formula such as H2O, Ca(OH)2, or C6H12O6 and calculate average molar mass, element breakdown, and percent composition.
Open calculatorFormula and Mass Tools
Use this cluster for molecular formula, molecular weight, molar mass, monoisotopic exact mass, isotope pattern prediction, formula-to-structure lookup, and grams-to-moles calculations.
Quick answer: use formula tools when you have a chemical formula, and SMILES tools when you have a structure string or a compound copied from MolDraw.
Choose a Formula or Mass Tool
SMILES to Molecular Formula
Paste a SMILES string and fetch the molecular formula with PubChem metadata.
Open converterSMILES to Molecular Weight
Convert SMILES to molecular weight, formula, IUPAC name, and PubChem CID when available.
Open converterExact Mass Calculator
Calculate monoisotopic exact mass from a chemical formula using common isotope masses.
Open calculatorMass Spectrum Predictor
Estimate isotope pattern peaks, molecular ion region, monoisotopic mass, and average mass.
Open predictorMolecular Formula to Structure
Search a formula such as C9H8O4 and compare multiple PubChem structure candidates.
Open searchGrams to Moles Calculator
Convert grams to moles or moles to grams using molar mass calculated from the formula.
Open calculatorWhen to Use Molecular Weight vs Exact Mass
- Molecular weight uses standard atomic weights and is best for molarity, solution prep, and classroom calculations.
- Exact mass uses monoisotopic masses and is commonly used in mass spectrometry and formula confirmation.
- SMILES to formula/weight is useful when a structure string is already available from MolDraw or a database.