That's a huge question. There are 1 billion cells for every tissue gram in weight, so that's 70 trillion if you weigh 70 kilograms. Different cells live for different lengths of time, some for a few hours, some for a few days and so on. Nobody knows for sure but say on average you replace all your cells every seven years, that's 10 trillion each year, 27 billion each day, that's 18.75 million every minute.
