How many miles are in a pair of running shoes?

I'm getting excited to start running outside again!  The weather is turning warmer and the snow and ice is nearly gone already!  So my question is as posted in the topic- how many miles can a pair of running shoes go?   I got my current running shoes at the beginning of December, so I'm guessing that they should be good for a while yet, but it's something I want to keep in mind.

Also, do you think it hurt my shoes that I've been wearing them for weight training at the gym?  I have separate shoes now for the gym just cuz my runners will be spending more time outside now, but I'm wondering if the weight routine took additional life out of my shoes.

Thanks for the help and advise!

I have heard about 500 miles for a good pair, which for a lot of runners equate to about 6 months. It might be more for lighter peope, and less for big people.

I am could be wrong though, I often am.....

Not sure if your weight routine took "life" out of your running shoes. But I have heard to never use your running shoes for anything except running & walking. Glad to see you got separate shoes for the gym!

Thanks guys.   Yeah I think 500 miles is about what I've heard too.  I'm pretty sure tho that I haven't covered that kind of ground in 6months tho!  Maybe I can push it to 8 or 10months.... kinda like how you put off changing the oil in your car LOL

The size of the person shouldn't make a difference on the wear on your shoes IF you have the right shoe for your person! 

I could tell a difference on my first pair at about 300 miles.  I know other runners that switch every 300, although that does seem to be the low end of the scale.

Here is a link to an article on when to replace shoes, and how to spot if they are worn (and, apparently, body weight does indeed play a part): running shoes

Since it's still evil rain/snow here in Toronto, I haven't quite gotten to the running and biking yet...

however my two pairs of running shoes are both several years old and have a bit of wear, is it bad for my feet if I keep using them or should I get a new pair?

custard - I suggest getting a new pair of shoes. You probably aren't getting the correct foot support from your current pair.