Seine vs. Thames: Which River Is Wider?

The River Thames is wider on average than the River Seine.

Average Widths

• River Thames (London reach): ~250–300 meters (820–980 ft) through central London, widening significantly downstream toward the estuary (up to 8 km / 5 mi at the Nore).
• River Seine (Paris reach): ~100–200 meters (330–650 ft) through central Paris, constrained by stone quays. It widens modestly downstream but remains narrower than the Thames estuary.

Why the Difference?

• Tidal Range: The Thames has a large tidal range (~7 m / 23 ft at London Bridge), creating a broad, dynamic intertidal zone and a funnel-shaped estuary. The Seine's tidal influence is damped by locks and weirs upstream of Rouen; its tidal range at Paris is only ~1–2 m.
• Geology & History: The Thames flows through a wide, post-glacial valley; the Seine is incised into a narrower chalk plateau.
• Engineering: Paris's Seine is heavily canalized with vertical quay walls since the 17th–19th centuries, fixing its width. London's Thames retains more natural, sloping foreshores in places.

Both are iconic, navigable, tidal urban rivers—but the Thames is the broader waterway.