Molecular Weight Calculator with Composition Table
Parse a chemical formula containing element symbols, subscripts, parentheses, square brackets and hydrate dots. The result reports molar mass, atom counts, element contributions and percent composition.
Chemical formula
Molecular weight and composition
molecular weight calculator: formulas, interpretation and worked use
This molecular weight calculator validates every element symbol and grouping multiplier. It displays the arithmetic contribution of each element so the result can be independently reproduced.
Transparent calculation steps
The molecular weight calculator displays the intermediate values used in the result so users can audit the calculation rather than receiving an unexplained answer.
Input validation and edge cases
Impossible, incomplete and non-finite inputs are rejected with a specific message. Boundary cases are handled explicitly instead of being silently rounded into a misleading result.
Units and precision
Where units apply, inputs are converted to a consistent internal basis before the formula is evaluated. Results retain enough precision for checking and are then formatted for practical reading.
Worked interpretation
The result panel separates the primary answer, supporting quantities and a formula trace. This makes the calculator suitable for checking homework, planning scenarios and comparing alternatives.
Formula syntax
Element symbols are case-sensitive. A capital letter starts a symbol and an optional lowercase letter completes it; numeric subscripts follow elements or closed groups.
Percent composition
Each element contribution is divided by total molar mass. Percentages should sum to approximately 100 percent, subject only to display rounding.
Formula parsing and atomic composition
The molecular weight calculator parses element symbols, numeric subscripts, parentheses and common hydrate-dot notation, then multiplies each element count by its stored standard atomic weight. Capitalization matters because Co is cobalt while CO represents carbon and oxygen. Parenthetical groups are expanded before totals are calculated, so Ca(OH)₂ contains one calcium, two oxygen and two hydrogen atoms.
Mass interpretation and formula limits
The molecular weight calculator reports grams per mole for a neutral formula composition. Standard atomic weights are representative values and may vary slightly with isotopic composition; a precise isotopologue requires isotope-specific masses. Charges do not materially change ordinary molar mass but must be written in supported notation so they are not mistaken for subscripts. The parser validates all element symbols against the 118-element table and rejects unmatched brackets, zero multipliers and unknown symbols rather than silently ignoring them.
Can it parse hydrates?
Yes. Use a middle dot or period, such as CuSO4·5H2O.
Does it understand parentheses and brackets?
Yes. Nested groups are parsed and multiplied by their following subscripts.
Why can atomic weights differ slightly elsewhere?
Published standard atomic weights can be represented with intervals or rounded conventional values. This calculator uses the displayed fixed table for reproducibility.