20 doses at 15 mg a dose equals how many oz?

20*15mg=300mg

https://www.google.com.au/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=mg%20to%20ounces

1mg=0.0000335274 oz

$${\mathtt{0.000\: \!035\: \!274}}{\mathtt{\,\times\,}}{\mathtt{300}} = {\mathtt{0.010\: \!582\: \!2}}$$   ounces

15mg x 1g/1000mg x 1oz/28.3495g = 0.00053

0.00053 x 20 = 0.011 doses