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Multiply each element’s atomic weight by how many atoms of it the formula contains, then add them up. Water (H₂O) is 2 × 1.008 + 15.999 = 18.015 g/mol.

טעקסט פֿאַרבelement symbols with optional counts, nested brackets and a leading multiplier for hydrates. Ca(OH)2 is read as one calcium, two oxygen and two hydrogen; CuSO4.5H2O includes five waters

Numerically they are the same value. Molecular weight (or molecular mass) is a relative figure in daltons for one molecule; molar mass is the mass of a mole in grams per mole. Both equal the summed atomic weights.

Use a dot before the water group: CuSO4.5H2O. The leading 5 multiplies the H2O, adding five waters of crystallisation, and the calculator returns 249.68 g/mol for that hydrate.

פֿאַר יעדער עלעמענט גיט עס דעם עלעמענטן טייל פֿון דער גאַנץ מאַס. אין וואַסער איז אָקסיגענ 88.8% און הידראָגען 11.2%; אין גלוקאָסע איז קאַרבאָנע 40.0%, הידראָגען 6.7% און אָקסיגענ 53.3% — נוצלעך פֿאַר דער עפּיריקאַלער פֿאָרמולע און פֿאַר די קלאָרײט־אַרבעט.

Every element symbol must be capitalised correctly (Co is cobalt, but CO is carbon plus oxygen), and only real elements are accepted. Check for lowercase symbols, unmatched parentheses or typos if you see a parse error.

Yes — wrap the group in parentheses with its multiplier, like Ca(OH)2 or (NH4)3PO4. The parser expands the parentheses and multiplies the enclosed atoms, so ammonium phosphate sums correctly across all three ammonium groups.