From Destinypedia, the Destiny wiki
Every player's character has a Vault, where they can store items, namely up to 20 armor pieces, 20 weapons, and 20 general items (shaders, emblems, ships, Sparrows, etc.). The space will be upgraded to 24 armor pieces, 36 weapons, and 24 general items in a future update, albeit at the expense of the comparison feature on the Xbox 360 and Playstation 3 versions.
The Vault in Destiny 2 previously featured 300 slots for any type of item or gear, instead of fixed areas for armor, weapons and general items. It was upgraded to 500 slots with Update 2.0, which went live the week before Forsaken.