Depends very much on the field, the country and the network (google, search, content). I use the following benchmarks for good CTR's on the search network: Software ~2% Ringtones ~3% Price comparison sites ~6% Branded goods ~10-20% These numbers are not absolute but are a standard that I use. The CTR varies greatly between products and also varies within each category. I've had software with a 5% CTR and other software products with a 0.3% CTR. Ad rank is also a factor (places 1-6 generally get better CTR's than 7-10 although some will disagree with me on this point). You can have a 1:1.5 ROI with a 5% CTR and a 1:5 ROI with 1%. In summation, the bottom line is what counts!