that's about the size of it

That sums up the situation; that’s how things are. For example, So he’s going to resign next month?—Yes, that’s about the size of it, or Mary’s applying to all those colleges?—That’s about the size of it. A mid-19th century British expression that soon crossed the Atlantic, it appeared in Mark Twain’s Tramp Abroad (1880): “‘Bloodshed!’ ‘That’s about the size of it,’ I said.”