"Results show that the doubling time early in the epidemic in Wuhan was 2.3–3.3 days. Assuming a serial interval of 6–9 days, we calculated a median R0 value of 5.7"

https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article

A herd immunity strategy involving fast immunization by continuing business as usual would then involve an R0 > 5.

There have been several studies that have come up with different numbers. I guess we can calculate some interesting stuff based on the range, but it's a really big range (I've seen somewhere in the range of 1.5 to 7 in various articles/studies).