Only 0.050% use the Imperial system globally as their standard measurement system and 99.95% of the world uses the Metric system.
There are only 3 countries that use the imperial system and every other country is using the metric system. Maybe one day the United States will switch over and there's discussions of Liberia switching back over. So what percentage though of the worlds population actually uses the Imperial system?
So total there is just under 400 million people using the Imperial Measuring system: 399,992,937. The worlds total population according to World Population Review is 7,922,312,800 persons globally, out of that only 400 million are using the Imperial System and the rest are using the Metric system so we have 399,992,937/7,922,312,800 = 0.050%
Maybe one day the USA will adapt with the rest of the world.