Take a look at
Black-Scholes. There are online calculators:
http://www.mystockoptions.com/black-scholes.cfmSome knowledge gathering would be nice, mine is limited.
Here is some data to play with:
Symbol: BTCGARDEN, Since: 03.08.2013 (7 days), N = 1430 (trades), Mean: 0.01609, Square: 0.00000, Volatility: 0.00072
Symbol: BTCGARDEN, Since: 11.07.2013 (30 days), N = 3145 (trades), Mean: 0.01607, Square: 0.00000, Volatility: 0.00055
Symbol: LABCOIN, Since: 03.08.2013 (7 days), N = 3317 (trades), Mean: 0.00149, Square: 0.00000, Volatility: 0.00018
Symbol: LABCOIN, Since: 11.07.2013 (30 days), N = 7189 (trades), Mean: 0.00192, Square: 0.00000, Volatility: 0.00065
Symbol: ACTIVEMINING, Since: 03.08.2013 (7 days), N = 1812 (trades), Mean: 0.00571, Square: 0.00000, Volatility: 0.00044
Symbol: ACTIVEMINING, Since: 11.07.2013 (30 days), N = 8274 (trades), Mean: 0.00634, Square: 0.00000, Volatility: 0.00133
Symbol: COGNITIVE, Since: 03.08.2013 (7 days), N = 136 (trades), Mean: 0.39382, Square: 0.00261, Volatility: 0.05109
Symbol: COGNITIVE, Since: 11.07.2013 (30 days), N = 1498 (trades), Mean: 0.63677, Square: 0.03166, Volatility: 0.17792
Symbol: COGNITIVE, Since: 12.05.2013 (90 days), N = 2490 (trades), Mean: 0.42228, Square: 0.09574, Volatility: 0.30942
Symbol: COGNITIVE, Since: 10.08.2012 (365 days), N = 3354 (trades), Mean: 0.32091, Square: 0.10075, Volatility: 0.31741
Symbol: BASIC-MINING, Since: 03.08.2013 (7 days), N = 447 (trades), Mean: 0.33758, Square: 0.00458, Volatility: 0.06769
Symbol: BASIC-MINING, Since: 11.07.2013 (30 days), N = 2439 (trades), Mean: 0.52844, Square: 0.02554, Volatility: 0.15982
Symbol: BASIC-MINING, Since: 12.05.2013 (90 days), N = 3990 (trades), Mean: 0.37648, Square: 0.05436, Volatility: 0.23316
Symbol: BASIC-MINING, Since: 10.08.2012 (365 days), N = 4728 (trades), Mean: 0.32338, Square: 0.06112, Volatility: 0.24723
Symbol: ASICMINER-PT, Since: 03.08.2013 (7 days), N = 1175 (trades), Mean: 3.82851, Square: 0.04996, Volatility: 0.22351
Symbol: ASICMINER-PT, Since: 11.07.2013 (30 days), N = 5027 (trades), Mean: 4.25488, Square: 0.11717, Volatility: 0.34230
Symbol: ASICMINER-PT, Since: 12.05.2013 (90 days), N = 16432 (trades), Mean: 2.15878, Square: 4.10140, Volatility: 2.02519
Symbol: ASICMINER-PT, Since: 10.08.2012 (365 days), N = 20757 (trades), Mean: 1.73078, Square: 3.94292, Volatility: 1.98568
It's up to X days, but possibly less than X days. I used N ticks as input. A volatility of 1.98 is equal to 198 %.
No guarantee for correctness.
Edit: Rounded numbers - I went a similar route as the following to calculate to volatility:
http://www.wikihow.com/Calculate-Historical-Stock-Volatility