Here's how we calculate it:

* Carbon (C): Atomic weight is 12.01 g/mol

* Oxygen (O): Atomic weight is 16.00 g/mol

Since carbon dioxide has one carbon atom and two oxygen atoms, we add their atomic weights together:

12.01 g/mol (C) + 2 * 16.00 g/mol (O) = 44.01 g/mol