The answer to this question probably generates more confusion than any other single aspect of WiMAX.  In the early days of WiMAX it was common to see statements in the media describing WiMAX multipoint coverage extending 30 miles.  In a strict technical sense (in some spectrum ranges) this is correct, with even greater ranges being possible in point to point links.  In practice (and especially in the license-free bands) this is wildly overstated especially where non line of sight (NLOS) reception is concerned. 

Due to a variety of factors explained in more detail in other FAQ answers, the average cell ranges for most WiMAX networks will likely boast 4-5 mile range (in NLOS capable frequencies) even through tree cover and building walls.  Service ranges up to 10 miles (16 Kilometers) are very likely in line of sight (LOS) applications (once again depending upon frequency).  Ranges beyond 10 miles are certainly possible, but for scalability purposes may not be desirable for heavily loaded networks.  In most cases, additional cells are indicated to sustain high quality of service (QOS) capability.  For the carrier class approach, especially in regards to mobility, cells larger than this seem unlikely in the near future.  The primary WiMAX focused US carrier Clearwire has stated that its cell sites are planned at about 1.5 miles apart for mobile purposes.  This choice is clearly one intended to meet NLOS requirements.  In licensed frequencies, expect similar performance or better for WiMAX than in traditional cellular systems.