Molecular weight of any formula, with element breakdown and mole conversion
| Element | Atomic Mass (g/mol) | Count | Subtotal (g/mol) |
|---|
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Water | H2O | 18.015 |
| Methane | CH4 | 16.043 |
| Ammonia | NH3 | 17.031 |
| Nitrogen gas | N2 | 28.014 |
| Oxygen gas | O2 | 31.998 |
| Hydrochloric acid | HCl | 36.458 |
| Sodium hydroxide | NaOH | 39.997 |
| Ethanol | C2H5OH | 46.069 |
| Carbon dioxide | CO2 | 44.009 |
| Table salt | NaCl | 58.440 |
| Baking soda | NaHCO3 | 84.006 |
| Sulfuric acid | H2SO4 | 98.072 |
| Limestone | CaCO3 | 100.086 |
| Slaked lime | Ca(OH)2 | 74.092 |
| Rust | Fe2O3 | 159.687 |
| Aluminum sulfate | Al2(SO4)3 | 342.132 |
| Magnesium nitrate | Mg(NO3)2 | 148.313 |
| Potassium permanganate | KMnO4 | 158.032 |
| Copper(II) sulfate, anhydrous | CuSO4 | 159.602 |
| Copper(II) sulfate pentahydrate | CuSO4·5H2O | 249.677 |
| Aspirin | C9H8O4 | 180.159 |
| Glucose | C6H12O6 | 180.156 |
Values use IUPAC 2021 conventional atomic weights (C 12.011, H 1.008, O 15.999, S 32.06, Cu 63.546). Your textbook's table may differ in the third decimal if it rounds differently.
Type a formula, get grams per mole. The calculator parses the formula the way your chemistry teacher does: each element symbol carries a count (no subscript means one), parentheses distribute their multiplier across everything inside them, a leading coefficient multiplies the whole group, and a hydrate dot adds waters of hydration. It then sums count × atomic weight for every element and shows the work.
M = Σ (atomic weight × atom count). For C6H12O6 that's 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 72.066 + 12.096 + 95.994 = 180.156 g/mol. For a hydrate, CuSO4·5H2O = 159.602 + 5 × 18.015 = 159.602 + 90.075 = 249.677 g/mol. The grams-to-moles card divides mass by the result: n = m ÷ M, and moles × 6.022 × 10²³ gives particle count.
Enter the formula with proper capitalization (Co is cobalt, CO is carbon monoxide, and the calculator will not guess for you). Parentheses and multipliers work to any depth, so K4Fe(CN)6 and CH3(CH2)3CH3 both parse. Click any example chip to load it. Edit the mass field and the mole card converts instantly; type into the mole field instead and it works in reverse.
How many moles are in 25.0 g of glucose? Molar mass first: 180.156 g/mol from the table above. Then n = 25.0 ÷ 180.156 = 0.1388 mol, which holds 0.1388 × 6.022 × 10²³ ≈ 8.36 × 10²² molecules. Now run it backward for a lab prep: to measure out 0.75 mol of NaCl you'd weigh 0.75 × 58.440 = 43.83 g.
One caution that trips every first-year student: molar mass (g/mol per formula unit) and molecular weight (dimensionless, from unified atomic mass units) are the same number with different labels. Where they diverge is ionic salts, which form formula units rather than molecules; the number still works identically for stoichiometry.
Molar mass is the mass of one mole of a substance, in grams per mole (g/mol). Numerically it equals the sum of the atomic weights of every atom in the chemical formula: water (H2O) is 2 × 1.008 + 15.999 = 18.015 g/mol, and glucose (C6H12O6) is 6 × 12.011 + 12 × 1.008 + 6 × 15.999 = 180.156 g/mol. One mole always contains 6.022 × 10²³ particles, so molar mass is the bridge between grams on a scale and molecules in a flask.
Write out the formula, list each element with its count (multiplying through any parentheses), look up each element's atomic weight, multiply by the count, and add the subtotals. For Ca(OH)2: calcium 40.078, plus 2 × oxygen (15.999), plus 2 × hydrogen (1.008), which totals 74.092 g/mol. The calculator automates exactly this, including nested groups like Al2(SO4)3 (342.132 g/mol).
18.015 g/mol. Two hydrogens at 1.008 each plus one oxygen at 15.999 sum to 18.015 grams per mole, so one mole of water weighs 18.015 grams, about 18 milliliters.
Multiply the water count through the whole H2O unit and add it to the anhydrous salt. Copper(II) sulfate pentahydrate is CuSO4 (159.602 g/mol) plus 5 × H2O (5 × 18.015 = 90.075), totaling 249.677 g/mol. The calculator accepts the dot written as ·, ., *, or ~.
Divide mass by molar mass: moles = grams ÷ g/mol. For 25.0 g of glucose, 25.0 ÷ 180.156 = 0.1388 mol. Going the other way, grams = moles × molar mass, so 0.75 mol of NaCl weighs 0.75 × 58.440 = 43.83 g. Multiply moles by 6.022 × 10²³ if you need particle counts.