What size desk mat should I buy?

The most common sizes among top-rated options run about 31.5" x 15.7" for a single-monitor setup with mouse and keyboard room. If you want full-width coverage for a wide desk or dual monitors, look at 36" x 17" or extended 47" options. Measure your usable desk depth first, most complaints in customer reviews come from mats that overhang or sit too close to the edge.