There's a calculation for their weight - measure in meters for this one

Girth squared x length x 69.3 = weight in Kg
0.95 x 0.95 x 1 = 0.9025 x 69.3 = 62.5Kg (or 65.8 if the measurements are the other way round)
We normally aim for between 70 and 85Kg liveweight for them to go and I reckon on getting about half the liveweight back in joints and cuts.
Deadweight drops to between 70-80% of the liveweight, and weight of cuts is normally 70-80% of the deadweight.
For feed, I'd be tempted to stick somewhere between 4 and 5 lbs per day, if they're lying around inside their arcs and not doing much because of the rotten weather you could stick to the lower amount.
HTH
Karen