Standing in an aisle, uncertain whether there is paprika at home, you have two options and both are bad: buy it and own three, or skip it and cook without. The information you need exists — it is on a shelf eight miles away.
Precision is not the goal
A pantry inventory does not have to be accurate to the gram to be useful. Knowing that something is roughly full, half, low, or gone answers the aisle question completely, and it is a level of bookkeeping a household will actually keep up with.
The moment of truth is putting it away
Any inventory that depends on remembering to update it after cooking will drift within a fortnight. The reliable moment is unpacking the groceries, because that is already an activity where every item passes through your hands one at a time.