Originally Posted by contango

I weigh about 250 and I've seen estimates that range from 40-80 calories per mile. Obviously a mile of freewheeling downhill takes almost no effort, climbing a big hill takes more.

26 miles x 40 cal/mile = 1040 cal. 26 miles x 80 cal/mile = 2080 cal.

Personally I figure without some specific means of measuring your power output there's no point guessing what difference it makes to ride on gravel or tarmac of different grades or whatever else.