Empirical Formula Calculator

Enter the mass or percentage composition and atomic weight for each element in the compound.

Element Symbol

Mass/Percent

Atomic Mass (u)

Element Symbol

Mass/Percent

Atomic Mass (u)

Element Symbol (Opt)

Mass/Percent

Atomic Mass (u)

Result:

Understanding the Empirical Formula

The empirical formula of a chemical compound is the simplest whole-number ratio of atoms of each element present in the compound. Unlike the molecular formula, which tells you the exact number of atoms (like C₆H₁₂O₆ for glucose), the empirical formula provides the most reduced form (CH₂O).

How to Calculate It Manually

Obtain the Mass: Start with the mass (in grams) of each element. If you are given percentages, assume a 100-gram sample so that the percentage becomes the mass (e.g., 40% becomes 40g).
Convert to Moles: Divide the mass of each element by its atomic molar mass (found on the periodic table).
moles = mass / atomic mass
Find the Mole Ratio: Divide all the mole values by the smallest mole value calculated in the previous step.
Convert to Whole Numbers: If the results are not whole numbers (e.g., 1.5 or 1.33), multiply all ratios by the same small integer (2, 3, 4, etc.) to achieve the simplest whole-number ratio.

Realistic Example: Ascorbic Acid (Vitamin C)

A sample of Vitamin C contains 40.92% Carbon (C), 4.58% Hydrogen (H), and 54.50% Oxygen (O).

Moles of C: 40.92 / 12.01 = 3.407
Moles of H: 4.58 / 1.008 = 4.544
Moles of O: 54.50 / 16.00 = 3.406

Dividing by the smallest (3.406):

C: 3.407 / 3.406 ≈ 1
H: 4.544 / 3.406 ≈ 1.33
O: 3.406 / 3.406 = 1

To get whole numbers, multiply by 3: C₃H₄O₃. This is the empirical formula.