How many masks will be needed in the USA during the COVID-19 outbreak?

There’s an interesting data point in a 3M press release today;

…this week, we secured approval from China to export to the U.S. 10 million N95 respirators manufactured by 3M in China.

10 million feels a big number. But it’s sadly a blip. Current government estimates indicate that the USA will require some 3.5 billion face masks though the course of the COVID-19 outbreak.