How does it parse parentheses and hydrates like CuSO4·5H2O?

The formula is tokenized character by character with a parenthesis stack, so nesting works to any depth: Ca(OH)2 expands the (OH) group twice before adding it, and K4[Fe(CN)6] resolves the inner (CN)6 first, then the outer bracket. A hydrate dot — written as ·, •, *, or . — splits the formula into parts, and a number right after the dot multiplies that whole part, so CuSO4·5H2O adds five waters: one Cu, one S, nine O (4 + 5), and ten H. If a bracket is left open or a symbol is not a real element, you get a specific error rather than a wrong number.

Which atomic weights do you use, and why might they differ from another tool?

We use the 2021 IUPAC conventional standard atomic weights — the single representative value per element, the same set on a current periodic table (H 1.008, C 12.011, O 15.999, and so on). Some calculators use older 4-figure values or different rounding, which is why you can see a result differ by a few hundredths in the last digit. For most elements the difference is well under 0.1%. We report molar mass to four significant figures so you see where any rounding lands.

How is the mass percent of each element calculated?

For each element, mass contribution = (number of atoms) × (atomic weight), and mass percent = that contribution ÷ total molar mass × 100. For water the oxygen row is 15.999 ÷ 18.015 ≈ 88.8% and hydrogen is the remaining 11.2%, which is why the table rows always add up to 100%. The rows are sorted heaviest-contribution first, so the element driving most of the mass is at the top — handy for spotting that, say, the metal dominates a salt's weight.

Why doesn't my result match the number on the reagent bottle?

A bottle's labeled formula weight is usually for the exact form in the bottle, including water of crystallization. If the bottle says copper(II) sulfate pentahydrate, enter CuSO4·5H2O (≈249.69), not anhydrous CuSO4 (≈159.61) — they differ by the five waters. Also check that you matched the bottle's hydration state and that capitalization is right: Co is cobalt, but CO is carbon monoxide. Enter exactly what the label's formula shows and the numbers line up.

Weigh out a reagent for a 0.25 mol prep

Your protocol calls for 0.25 mol of sodium chloride. You type NaCl, read the molar mass (58.44 g/mol), switch the converter to Moles → mass, enter 0.25, and get 14.61 g — the number you dial into the balance. No scribbling n = m/M on a paper towel, no transposing a digit between the calculation and the weighing boat.

Make up a hydrate stock solution correctly

You need copper(II) sulfate solution but the shelf only has the pentahydrate. Entering CuSO4·5H2O gives 249.69 g/mol, not the 159.61 of anhydrous CuSO4, so the mass you weigh accounts for the five waters of crystallization. Use the wrong molar mass here and your solution is off by more than a third — the breakdown table shows exactly how much of that 249.69 is water.

Check a molecular-weight homework answer

A worksheet asks for the molar mass of glucose, C6H12O6. You type it, read 180.16 g/mol, and the per-element table confirms 6 carbons (72.07 g/mol), 12 hydrogens (12.10), and 6 oxygens (95.99). When a student's answer is off, the breakdown pinpoints which element's count they miscounted instead of just flagging the total as wrong.

Find the percent composition of a compound

A gen-chem question asks for the mass percent of nitrogen in ammonium sulfate. Enter (NH4)2SO4 and the table reads the N row directly — about 21.2% — with the percentages summing to 100 so you can trust the split. No separate "percent composition calculator" needed; it is the same breakdown that comes with every molar mass result.

Verify an unfamiliar coordination complex

You meet K4[Fe(CN)6] in a problem set and aren't sure how the nested brackets expand. Pasting it returns the molar mass (368.35 g/mol) and a breakdown showing 4 K, 1 Fe, 6 C, and 6 N — confirming the inner (CN)6 multiplied correctly before the outer bracket, so you can move on to the actual chemistry.

Molar Mass Calculator — molecular weight, element breakdown & mole conversion

Type any chemical formula — get molar mass, a per-element mass-percent table, and mass↔mole conversion. IUPAC weights, browser-only.

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

Chemical formula

Try:

Molar mass · C6H12O6

180.156 g/mol

Composition by element

Element	Atoms	Atomic wt.	Mass (g/mol)	Mass %
O	6	15.999	95.994	53.28%
C	6	12.011	72.066	40%
H	12	1.008	12.096	6.71%

Mass ↔ amount of substance

Mass (g)

Amount of substance

0.00555 mol

What this tool does

Paste a chemical formula and read its molar mass to four significant figures, plus the full per-element breakdown students and lab techs actually need. The parser handles real reagent notation, not just toy examples: multi-digit subscripts (C6H12O6), nested parentheses and brackets (Ca(OH)2, K4[Fe(CN)6]), group multipliers ((NH4)2SO4), and hydrate dots (CuSO4·5H2O, Na2CO3·10H2O). Every element row shows its atom count, atomic weight, mass contribution, and mass percent — and the percentages always sum to 100, so you can sanity-check a composition at a glance. Atomic weights are the 2021 IUPAC conventional standard values, the same numbers printed on a modern periodic table, so your answer matches the textbook instead of drifting a few hundredths. A built-in converter turns grams into moles (n = m / M) or moles back into grams, so weighing out a reagent for a 0.5 mol prep is one input away. Everything runs in your browser — no formula you type is ever uploaded — and the formula is encoded in a shareable URL so you can send a colleague the exact calculation.

Tool details

Input: Text + Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 12 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Student; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Molar Mass Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Weigh out a reagent for a 0.25 mol prep
Your protocol calls for 0.25 mol of sodium chloride. You type NaCl, read the molar mass (58.44 g/mol), switch the converter to Moles → mass, enter 0.25, and get 14.61 g — the number you dial into the balance. No scribbling n = m/M on a paper towel, no transposing a digit between the calculation and the weighing boat.
Make up a hydrate stock solution correctly
You need copper(II) sulfate solution but the shelf only has the pentahydrate. Entering CuSO4·5H2O gives 249.69 g/mol, not the 159.61 of anhydrous CuSO4, so the mass you weigh accounts for the five waters of crystallization. Use the wrong molar mass here and your solution is off by more than a third — the breakdown table shows exactly how much of that 249.69 is water.
Check a molecular-weight homework answer
A worksheet asks for the molar mass of glucose, C6H12O6. You type it, read 180.16 g/mol, and the per-element table confirms 6 carbons (72.07 g/mol), 12 hydrogens (12.10), and 6 oxygens (95.99). When a student's answer is off, the breakdown pinpoints which element's count they miscounted instead of just flagging the total as wrong.
Find the percent composition of a compound
A gen-chem question asks for the mass percent of nitrogen in ammonium sulfate. Enter (NH4)2SO4 and the table reads the N row directly — about 21.2% — with the percentages summing to 100 so you can trust the split. No separate "percent composition calculator" needed; it is the same breakdown that comes with every molar mass result.
Verify an unfamiliar coordination complex
You meet K4[Fe(CN)6] in a problem set and aren't sure how the nested brackets expand. Pasting it returns the molar mass (368.35 g/mol) and a breakdown showing 4 K, 1 Fe, 6 C, and 6 N — confirming the inner (CN)6 multiplied correctly before the outer bracket, so you can move on to the actual chemistry.

Common pitfalls

Mixing up case in element symbols. Co is cobalt; CO is carbon monoxide; Cu is copper but CU is not an element. The parser is case-sensitive on purpose — an uppercase-only paste like "NACL" will fail rather than silently guess.
Forgetting the water of crystallization. A hydrate weighs more than its anhydrous form. Enter CuSO4·5H2O (249.69), not CuSO4 (159.61), when your reagent bottle says pentahydrate, or every mass you weigh out will be short.
Treating molar mass as exact to many decimals. Standard atomic weights carry uncertainty, so we report four significant figures. Quoting 180.156 g/mol for glucose implies a precision the underlying atomic weights don't have.

Privacy

Parsing, the atomic-weight lookup, the per-element breakdown, and every mass↔mole conversion run as plain JavaScript inside your browser tab. No formula you enter is uploaded, logged, or sent to any server, and there is no external API call. The one thing to know: the formula is encoded in the shareable URL (e.g. ?q=C6H12O6), so if you paste a share link somewhere, the destination's access log records that formula. Chemical formulas are not sensitive, but if you'd rather not, copy the result instead of sharing the URL.

FAQ

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Molar Mass Calculator — molecular weight, element breakdown & mole conversion

Composition by element

Mass ↔ amount of substance

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Molar Mass Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Weigh out a reagent for a 0.25 mol prep

Make up a hydrate stock solution correctly

Check a molecular-weight homework answer

Find the percent composition of a compound

Verify an unfamiliar coordination complex

Common pitfalls

Privacy

FAQ

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