My personal, scientific scale:
2/3/4/5 - probably one of the stronger guys on his block, in his office (assuming he is not in physical labor)
2+/4/5/6 - really fucking strong, one of the strongest guys at most average commercial gyms, strong for Tnation
3/4/6/7 - really, really fucking strong.
Big 3 - 2000lbs+, you could call my mother whatever you want and I smile and nod.