Molecular Weight Calculator
Type a formula — parentheses welcome — and read its gram-per-mole price with the percent composition alongside: the periodic table, doing arithmetic.
Molecular Weight Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Conventional IUPAC single-value weights (interval elements approximated)
- One level of parentheses; no nested groups, no hydrate dots
In short: Glucose, C6H12O6: 6×12.011 + 12×1.008 + 6×15.999 = 180.156 g/mol. The parser also opens brackets: Ca(OH)2 prices at 74.092000 g/mol and (NH4)2SO4 — two ammoniums against one sulfate — at 132.134000 g/mol. Water splits 11.190674% hydrogen by mass and 88.809326% oxygen: the atmosphere’s favourite molecule is mostly oxygen by weight.
Formula
MW = Σ count·atomic weight · symbols: [A-Z][a-z]? · one bracket level: Ca(OH)2, (NH4)2SO4
A formula is a shopping list: each element symbol carries a count, the molecular weight is the bill, and parentheses multiply a whole group at once — two hydroxides per calcium, two ammoniums per sulfate. Percent composition divides each element’s share of the bill by the total: the recipe by mass.
Worked Example
- Type the formula: symbols, counts, one bracket level.
- Read the molecular weight in g/mol.
- Read the element-by-element breakdown.
- Read the percent composition by mass.
C6H12O6 → 180.156 g/mol; (NH4)2SO4 → 132.134000; water: 11.190674% H, 88.809326% O by mass.
Strengths & Limits Of This Model
Where this engine is strong
- Itemised bill, not just the total
- Refuses with reasons, never guesses
Where it stops
- No charge or isotope pricing
- No mixtures or averages
Practical Use Cases
Feeding the mole pages
MW for moles and molarity
Solution prep
hydrate vs anhydrous prices
Checking coursework
the bill, itemised
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Molecular Weight Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why does Ca(OH)2 need parentheses?
Because the subscript binds the GROUP: calcium hydroxide is one calcium plus TWO hydroxides — two oxygens and two hydrogens — not one oxygen and Ca(OH)2 read left to right. The parentheses make the multiplier unambiguous, and the parser prices the bracketed unit once, then times two: 74.092000 g/mol.
How does the parser handle (NH4)2SO4?
It reads a group, then the count outside the bracket: two of (N + 4H), then one S and four O. That is 2×18.039 + 96.056 = 132.134000 g/mol — ammonium sulfate’s price. One level of parentheses keeps the grammar honest; nested brackets are refused rather than guessed at.
What are the atomic weights based on?
Conventional single-value standard atomic weights from the IUPAC tables — one number per element, chosen for normal terrestrial materials. Some elements (chlorine among them) actually span small intervals in nature because isotope mixes vary by source; the single value is a convention, and routine bench arithmetic is well inside its accuracy.
Why is water mostly oxygen by mass?
Hydrogen is the lightest atom on the table — it takes twelve of them to balance one oxygen’s 16/1-ish weight ratio. Two hydrogens against one oxygen still leaves oxygen holding 88.809326% of the mass. Percent composition is where lightweight counting tricks meet heavyweight mass honesty.
Can I price an ion like SO4 2-?
Price the formula SO4 and handle the charge separately — electrons are far too light for the balance (a mole of electrons weighs about 0.55 milligrams). Ions inherit the neutral formula’s price to within the fourth decimal, which is why the parser ignores charge notation and prices atoms.
Why is my hydrate’s price higher than the handbook’s anhydrous value?
Because the waters are IN the crystal and ON the scale: copper sulfate pentahydrate carries five waters at 90.075 g/mol extra. Either price the full hydrate — the waters are countable, so the parser’s arithmetic extends — or weigh the anhydrous salt and enter its price downstream. Consistency between what you weigh and what you enter is the whole game.
What does the parser refuse, and why?
Unknown symbols, empty input, zero counts, unclosed or unopened brackets — anything it would have to GUESS at. A parser that guesses prints confident nonsense; this one prints the reason instead. If your element is real but missing, the message says exactly how many elements the page knows.
How does this feed the rest of the category?
Every concentration downstream drinks the gram-per-mole price: the moles page divides mass by it, molarity divides again by litres, and the percent-solution page ties clinical percentages back to molar. One honest parse at the top of the chain keeps all of it honest.