According to Lees in this journal entry, Shackleton calculates that they will need their provisions to last for six months which, in fact, turns out to be a quite accurate estimate.
Orde-Lees Journal
Sunday, 26 March, 1916
Yesterday was bitterly cold in the tent. We passed all day in our sleeping bags. It was too cold on the hands to sew or write much, but we luckily now have most of the volumes of the Encyclopaedia Britannica brought up from Ocean Camp, which afford us all the greatest consolation in the way of reading and provide us with topics for discussion. We also have a few novels and books of exploration.
The temperature is not strikingly low as temperatures go down here but the terrific wind penetrates the flimsy fabric of our fragile tents and creates so much draught that it is impossible to keep warm within.
At supper last night our drinking water froze over in the pot in the tent before we could drink it. It is curious how thirsty we all are.
The cold tinned fish or tinned curried rabbit luncheon have now come to and end owing to the supply being exhausted, and we are reduced to a much more restricted diet - breakfast consisting of a cup of hot milk (3/4 oz. Trumilk Powder) and1/4 lb. dog pemmican; luncheon, one biscuit (1 1/2 oz.) and six lumps of sugar (1 1/4 ozs.); for supper we have nearly a pint of stewed seal containing about 8 ozs. to 10 ozs. of meat and that is all, a total of a pound, or 1 pound and a trifle over, per diem. This is the weight of a dog's daily ration of dog pemmican, but our pound contains only one quarter of that excellent and nourishing substance. Still it is sufficient to maintain health on, if not strength.
A few days ago Sir Ernest went through the whole of the available provisions and has decided to allow for a possible period of six months and the above dieting is the result of this proportioning. Unfortunately it involves the consumption, during that period, of the whole of our reserve sledging rations which we should especially want when we "break out" in the boats. We therefore frequently trust that our release from the pack may take place soon and especially that it may be in calm weather!
This dietary comprises the whole of our seal meat and even the twelve remaining dogs, which we reckon will provide two days meat each, but even then it leaves as many as 72 suppers unprovided for; for these we rely upon getting a few more seals yet, but as we have only got two during this month things do not look altogether too propitious.