how many miles?

I'm saving up to buy a bike computer/odometer, but until then, how do I know how far I've gone when I'm not biking on marked trails?

If you are on streets you can use any of the sites people use for running, like www.runningmap.com or www.mapmyrun.com.  There's probably 15 different ones. 

If you are on a trail in a park, check the park's website, or see if there are any local running or cycling clubs that have measured the distances and posted them online.  I know the StL Track Club has done that with some routes, so I would presume other clubs in other towns might do the same.

marconi,  Wal-mart use to sell a bicycle computer for 10.00, I think it carried a schwin name.  I used it until I could get a better one and it worked great.  Very simple to use and put on.

I recomend cateye computers when you go for a good one.

Here's one for $20 from Walmart: http://www.walmart.com/catalog/product.do?pro duct_id=5679632

Mapmyrun also has a sister site mapmyride.com that uses google maps.  I've mapped a few of my rides and find it to match my odometer (Cateye Astrale) really closely.  A 20 mile route was right on and a 52 miler was off by less than a mile.  I also like the elevation chart.

http://www.mapmyride.com/

http://www.gmap-pedometer.com  is from Google, the only one I tried and is great too!