What does "stacked three high" mean?

"The beds were stacked three high."

Does it mean they were stacked three feet high or three bunks high?

Solution 1:

'stacked n high' means n units are stacked one above another. In this instance, it means that three beds/bunks were stacked one above another. [This implies that the final height will be the height of 3 beds, but the relevant information is that there are 3 beds placed one above another.]

Note that it's also possible to use a unit of distance, e.g. 'the beds were stacked 3m. high'. In this case, the relevant information is that the final height of the stack is 3 meters; we don't know how many beds this amounts to without more information about the beds.

There's also a third usage, with units such as 'layer' or 'tier', e.g. 'the beds were stacked 3 tiers high'. Here, the relevant information is the number of tiers. Strictly speaking, without more information about the precise composition of each tier, we won't know either the final height or the number of beds. (For instance, a layer may be composed of 2 planks and 1 bed, in which case the final number of stacked beds will be 3, but the height will be the height of 3 beds plus 6 planks.) But it's probably most often the case that this simply means that 3 beds are placed one above the other, in which case the number of beds is 3, and the height is the height of 3 beds. So this usage is often interchangeable with the first: 'the beds were stacked three high' and 'the beds were stacked three layers high' will usually describe the same situation.