All beekeepers know that it is important to ensure that a colony has sufficient food for the winter, and if necessary will top up the stores in mid-winter by giving the bees some fondant or candy.
Most beekeeping books suggest that we estimate the amount of stores remaining by “hefting” the hive. i.e. by lifting the side to estimate the weight. I have never found it easy to estimate the stores in this way, and for several years have weighed my hives by modifying a portable digital luggage weighing scales, which cost about £12, to hook under one side of the hive. See http://tinyurl.com/nuufw2g. These scales indicate the maximum load (metric or imperial) when the hive is lifted up. This process is repeated on the opposite side of the hive, and the total hive weight is the sum of these two readings.
Using such a method, changes in hive contents can be followed over the winter. The initial autumn value of stores may be obtained from visual inspection of the hive or alternatively by weighing the individual components of the hive and subtracting this from the measured hive weights. I find that the typical weight of a wooden National hive without stores is ~17kg for a single brood box and ~22kg for brood and a half.
The graph below shows the variation in the estimated weight of stores for three colonies over a winter, and in addition to showing the weight of stores remaining, it gives some indication of the hive activity, Typically it shows a steady consumption of stores from October to December, followed by more rapid consumption in January and February, probably when the queen is starting to lay again, and then the hive weight increases in late March or April as the bees start foraging and the colony grows. The average rate of consumption of the stores for a hive is typically 0.5-0.7kg per week over the winter.