The amount of substance in a given sample of matter is defined as the number of distinct atomic-scale particles in it divided by the Avogadro constant NA.
The amount of substance is literally the sum of particles that make up the product.
The Particles may be molecules, atoms, particles and electrons depending on the context.
The value of Avogadro constant NA was defined as 6.02214076× 1023mol−1.
From a purely atomistic point of view, 1 mol = 6.02214076 × 1023 particles and thus the conversion constant is simply NA = 1.
The amount of substance is often referred to as the chemical amount.