ballpark estimate

Origin

This phrase vividly evokes the wide-open spaces of a baseball stadium, or "ballpark." Imagine a fan trying to guess the attendance at a game, or the score of a high-scoring match. You can't be precise, but you can get "in the ballpark" – meaning, close enough to the actual figure. The phrase soared in popularity during the mid-20th century, especially in American business and politics, when someone needed to give a quick, rough approximation without getting bogged down in exact numbers. It's a nod to that comfortable margin of error found within the broad confines of a baseball field.