More than 1.4 million copies were sold on the first day in the US, Canada and UK, per New York Times.
It's Penguin Random House's fastest-selling non-fiction book, beating Barack Obama's "A Promised Land".
"Spare," which went on sale Tuesday, has become the publisher's highest-selling non-fiction title on day one, with more than 400,000 copies sold in Britain alone.
His wife Michelle Obama's "Becoming", sold more than 725,000 copies on its first day and took a week to sell 1.4 million, per Penguin Random House.
Penguin Random House didn't immediately respond to a request for comment from Insider.