How long, in miles, is the River Thames?

The River Thames is approximately 215 miles long, making this the accurate measurement for the river's length. This distance includes its winding path through various landscapes, starting from its source in Gloucestershire, flowing through London, and emptying into the North Sea. The Thames is notable not only for its length but also for its historical significance, serving as an important waterway for trade and transportation throughout British history.

The other options do not reflect the correct length of the River Thames, as estimates of 150, 300, or 500 miles either underestimate or overestimate the true distance. This understanding of the River Thames is crucial for anyone studying geography or British history, as its dimensions play a significant role in the context of its impact on settlement and development in the surrounding areas.