Answer: Width ranges from 112 mi (180 km) in the west to 20 mi (32 km) in the east, between Dover England and Calais France. Swimmers are typically concerned with the narrowest point, and that question has two parts.
1. How far in miles:
The short answer is 25 miles. The English Channel is 20.3 miles wide at its narrowest point. The common start and end points for swimmers widens this a little to 20.6 miles wide, as the crow flies (lucky crow). Unlike crows, swimmers contend with tidal currents that weave them off-course. Weaving makes the actual distance across the channel closer to 25 miles for most swimmers. Some particularly lucky or experienced swimmers manage to swim direct, traveling only 21 miles. Unlucky swimmers have gotten caught in especially powerful tidal currents and end up swimming up to 30 miles to cross the English Channel.
2. How long in hours to swim:
The short answer is 14 hours. Time is a factor of speed and distance. Adam and I have swum together for many hours averaging 1.5 mph. At this swim rate, a bee-line (21 miles) for France will be a 14 hour swim. If we zig-zag (28 miles) it will be a 19 hour swim.
Here is a quick map mock-up of two swim routes and our projected swim times if we follow each route. For more swim route maps check out this link.