An Empirical Formula is the simplest formula that represents the whole number ratio between the elements in a compound.

Molecular formulas and empirical formulas are sometimes the same:

• The molecular formula for water is H₂O, a 2 to 1 ratio.
• Since the subscripts will not reduce H₂O is also water's empirical formula.

Molecular formulas and empirical formulas are sometimes different:

• The molecular formula for glucose is C₆H₁₂O₆, not a 1 to 1 ratio.
• Reduce the subscripts to the lowest form.
• The empirical formula for glucose is CH₂O, a 1 to 1 ratio.

Calculating empirical formulas:

• Subscripts in a chemical formula are usually thought of as a ratio of atoms.
• Subscripts can also be thought of as a ratio of moles.
• To determine an empirical formula, one must determine the mole ratio.

A mole is the number of atoms needed to equal the atomic mass of an element, therefore the atomic mass of an element in grams is equal to one mole of its atoms.