A mile in good walking speed would take about half an hour I reckon, so I reckon I walk about 4 miles a day, but I say it by how long I'm out cos the dog walks much further than me as he runs around, plays with dogs and walks around me. 10 miles would be about 5 hours walking, most people would never do that every day.
I think it's more important how long you are out instead of how far you walk. Don't worry, you sound like you walk your dog enough.

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I OWN A CHOCOLATE ROAN COCKER SPANIEL
RIP David xx Run free at the bridge. Love you always xx 19th February 2011
RIP Jack and Mickey xx Run free at the bridge. Love you forever xx 20th June 2011