The highest daily volatility ever was 15% and it's currently around 4%, according to https://bitvol.info/ . Two times the highest daily standard deviation ever doesn't seem so unreasonable.
That's the highest AVERAGE ROLLING 30 DAY volatility.
For example, on Dec 7, 2013, volatility between the high and the low was 54.6%. [1] However, it was lower for the other days of all 30 day periods that include that day, and averaged out to under 15%.
For example, on Dec 7, 2013, volatility between the high and the low was 54.6%. [1] However, it was lower for the other days of all 30 day periods that include that day, and averaged out to under 15%.
1 - https://www.coindesk.com/price/