The size of a propane tank for a house depends on the size of the house and the demand for propane at the house.
Most propane tanks for houses and residential propane tanks are between 250 gallons to 500 gallons of propane which usually lasts at least 1 month or 2 months between refills.
You typically have a regularly scheduled refill or top up on the propane tank every other month before you actually run out of propane.
But the propane tanks for houses should be between 250 gallons to 500 gallons depending on house size and how much propane the house needs to operate.