Generating a magnetic field

I'm trying to generate a magnetic field that's strong enough to be detectable (i.e., still stronger from the earth's field) at some distance away from where I'm generating it. I have a pretty simple setup with some current running through a wire wrapped around a nail, and I can detect it up to a couple of inches away. I was wondering what I could do to increase the range? I know the Biot-Savart law says I should increase current and reduce radius, but I was wondering if there are any other equations I should be looking at?

Thanks!