The formula for boron carbide is B4C, not B4C3. This is because boron carbide has a cubic crystal structure, in which each boron atom is surrounded by four carbon atoms, and each carbon atom is surrounded by four boron atoms. This results in a very strong and hard material, which is often used in abrasives and cutting tools.

If the formula were B4C3, this would indicate that there were three carbon atoms for every four boron atoms. This would result in a different crystal structure, and the material would not have the same properties as boron carbide.