With appropriate ground corrections 5 cm is pretty easy with the current US satellites. Sub-meter in real time is also fairly easy with the help of WAAS broadca

With appropriate ground corrections 5 cm is pretty easy with the current US satellites. Sub-meter in real time is also fairly easy with the help of WAAS broadcasts and good receivers. But if consumer hardware (like a typical $200 Garmin receiver) could reliably have sub-meter accuracy that would be a big improvement. But I'm no expert on the actual math of GPS.