This BMI chart calculator and comparison infographic by Visually will let you know how you're doing worldwide. Unfortunately, according to this chart, America is in pretty rough shape. The chart has listed them as having the second highest BMI average.
The chart is broken down into four different sections of BMI averages. It starts by listing countries with averages between 20-22.9 and reaches the average of 27 plus. It is stated in the chart that those with a BMI of 18.5-22.9 are in a healthy range.
At the bottom of the BMI chart there is a place that allows one to calculate their own results. This can give you an idea of how you compare against the worldwide statistics and even just the statistics within your specific country.