How much water do older toilet tanks hold?

Older toilet tanks typically hold between 3.5 to 7 gallons of water per flush, depending on the model and age. Many toilets manufactured before the 1990s used around 5 to 7 gallons, while those made in the early 1990s began to transition to lower volumes. In contrast, modern toilets generally use 1.6 gallons or less per flush to promote water conservation.