The total area of all constellations is the total area of the sky, which is exactly 4π steradians, or 4π × (180/π)2 = 129,600/π square degrees, or approximately 41,252.961 square degrees. The individual areas do not sum to this number due to rounding errors, which vanish when the areas are rounded instead to one decimal place.
Data from Wikipedia US page - "List of constellations by area"