What is the largest asteroid that crosses Earth's orbit?

To cross Earth's orbit” is something that has to be clarified. We call any asteroid that can come within 0.05 astronomical units or 7.5 million km of Earth potentially hazardous. read more

So, I take the term “crosses Earth’s orbit” in that sense. The largest potentially hazardous asteroid is (53319) 1999 JM8, which has a diameter of about 7 km. But it has no chance to impact Earth, and it won’t come particularly close in the 21st century. read more

An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids. read more