The #1 is the "standard", #10 the thickest, and #3 in between. My guess is the #10 would be 1-1/2". You might want to go to a hardware store or plumbing shop with your tape measure. If the flange is set properly on top of the finished floor the #1 should be just fine. If the flange is recessed below the finished floor, then you will need a thicker on. By all means do not get the type with the plastic funnel. These usually present a problem, especially with a 3" flange. The waxless seal is also a good option to consider.