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Formula Calculator

Find empirical & molecular formulas with step-by-step working

Ar values matched to your exam board
Composition breakdown 0%
Quick-fill examples
Element Percentage (%)
g/mol

Enter elements and values above, then press Calculate

Exam tip: This tool uses Ar values that match the GCSE and IB data booklets. Always show your working in exams — write the method, not just the answer.
Need mole calculations? Try the Moles Calculator → Look up Ar values with the Periodic Table → Read: The Mole Explained → Read: How to Find Empirical Formulas →
Find the value of x in a hydrated salt formula like CuSO4·xH2O. Enter the Mr of the anhydrous salt and the hydrated salt.

Enter Mr values above, then press Calculate

Exam tip: In heating experiments, the hydrated mass is the "before" and the anhydrous mass is the "after". Calculate Mr values from the formula, then use this tool to find x.
Need mole calculations? Try the Moles Calculator → Look up Ar values with the Periodic Table →