As the Model 3 is the world's best selling all-electric car (and plug-in car in general) with 300,885 units globally in 2019 (448,704 cumulative by the end of 2019) it's important to know from where the demand comes from.
Tesla officially revealed that the majority of over 150,000 (probably over 160,000) were sold in North America. The second biggest market was Europe, below 100,000 (probably around 95,000). The greater China region was third with less than 40,000.
A very positive sign is that in 2019, despite all the expansion in Europe and China, Tesla actually managed to increase its sales in North America by a noticeable amount, despite the phase-out of the federal tax credit in the U.S. and the lack of a long queue of orders like in 2018. That alone is a huge success.
We estimated that in 2019 Tesla sold some 158,925 Model 3 in the U.S. (up 13.7% year-over-year) and it seems that both the growth and volume is not far off - probably within 5% (nearly 8,000), or at least 10% (16,000), of the real number. Not bad, considering the lack of data over 12 months.
The year 2019 could be the best year for Tesla Model 3 sales, since in 2020 the company is introducing the Tesla Model Y in the U.S., which, depending on the ramp-up rate, might quickly offset Model 3 gains in China (through the Gigafactory 3).