Two of the fastest marathon courses on earth, two very different races. Here's every stat, side by side, to help you pick.
Indicative — based on GPX data. Both courses normalised to start at 0m.
✓ marks the better number on that stat.
Both are Majors, both are ballot-entry, and both draw fields well past 55,000 — but the courses differ meaningfully. Chicago is one of the flattest courses anywhere (45m of gain), while London carries slightly more elevation change (85m) across its Thames-side route past Tower Bridge and Canary Wharf. Chicago's course records (2:00:35 men, 2:09:56 women) are both faster than London's, reflecting that extra flatness.
The calendars split them by season: London in late April, Chicago in early October, so it's entirely possible to run both in the same year. If pure speed on a dead-flat American course is the goal, Chicago edges it; if you want the London crowds, the Cutty Sark start and a slightly more scenic route, London is the one to pick.