Walking with Weights

Question
How many calories do I burn (I am 145 pounds) by walking 2 miles at 4 miles per hour with a 3 pound weight in each hand?

Answer
People burn about 100 calories per mile, but it varies considerably from person to person, depending upon efficiency. The more you weigh the more you burn, and carrying hand weights can burn a few more calories. However, the extra calories from hand weights might increase risk of injury to the upper body.

You sound like you are in good shape, and if you have been carrying hand weights injury-free for some time, you are probably fine. But I would not suddenly add three pounds weights all at once. It may only add 5-10% more calories. You could gain that much or more without weights by gradually increasing speed and/or walking longer.