Why Use 4 Significant Figures for Avogadro’s Number?

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Although Avogadro's Number is named for Avogadro, he did not invent or discover it.
Although Avogadro’s Number is named for Avogadro, he did not invent or discover it.

Avogadro’s number (Avogadro’s constant) is the quantity of objects found in 1 mole of a sample. It is an exact number that is defined as 6.02214076×1023 mol−1. This is essentially the number of atoms in 12 grams of carbon-12.

However, for most chemistry calculations, you work with atomic masses, which are commonly reported using 4 significant figures.

When you perform calculations using significant figures, you use the smallest number of significant digits. So, if you are using a mass of carbon that is 12.01 grams/mole (4 significant figures), you use 6.022 x 1023 as Avogadro’s number (4 significant figures).