"Yes, we know - that's not a proper standard...."

The average mass is 68kg*, and the volume in cubic centimetres is V=453.95 x M **, where M is the mass in pounds (approx 150lb). Thus V = 453.95 * 150 = 68092 cubic centimeters or 0.068092 cubic metres.

Therefore, a balloon of about 850,000 cubic metres*** equates, in proper units of volume, to about 12.5 MSheep.

* "Resource use efficiency in food chains" - report to DEFRA, AEA Technology, Jan 2007

** "Wool Fibre Density of Shropshire Lambs" - Hardy, JI and Wolf, HW - J Anim Sci 1947. 6:72-82.

*** "The ATIC long Duration Balloon Project" - Advances in Space Research, 33:1763-1770 (doi:10.1016/j.asr.2003.05.018)