▲下面是《张道真英语用法》对你这个问题的相关用法：

表示长、宽、高可以用 by 字或 × 号：

The island measures about 25 miles by 12 miles. 岛的面积约为25英里长12英里宽。

The box measures approximately 26 inches long × 25 inches wide × l6 inches deep. 这个箱子约26英寸长，25英寸宽，16英寸高。

Each section is 2×2×1 metres in size. 每一块体积为2×2×l米。

▲你的三个句子的翻译：

The box measures 3 meters wide×2 meters deep×1 meter high. 这个箱子长3米、宽2米、高1米。

The room measures 6×4×5 metres. 这个房间长5米、宽4米、高3米。

The cave is 50 meters long×3 meters wide×2 metres high. 这个岩洞长50米、宽3米、高2米。

▲下面从其他资料引用的关于长宽高的表示法：

The room measures 6×6 metres. 这房间的面积为 6 米×6  米。

This desk measures 125 X 60cms. 这张桌子的尺寸是125×60厘米。

The picture measures 10 by 14 inches. 这张照片有10×14英寸大小。

The garage is 6 metres long and 3 metres wide. 汽车房长6米，宽3米。

The main bedroom measures 12ft by 15ft. 主卧室宽12英，长15英尺。

The new dock was 230 m long and 92 m broad. 新码头长230 米，宽92 米。

The tunnel is 10 metres wide and 600 metres long.  隧道宽10米，长600米。

The main bedroom measures 24ft by 18ft (24’ x 18’). 主人房长24英尺，宽18英尺。

The island measures about 30 miles by 50 miles. 这座岛长50英里，宽30英里。

The rectangle is 5 cm long and 1.9 cm wide. 这个长方形长5厘米，宽1.9厘米。

The plots each measure 10 metres by 20 metres. 这些地块每一块长20 米，宽10 米。

The classroom is 30 feet in length and 15 feet in breadth. 教室长30英尺，宽15英尺。

Lake Nyasa is 450 miles long by about 50 miles wide. 丽莎湖450英里长，约50英里宽。

The final dimensions of the pond were 14 ft × 8 ft. 这个池塘最后量出的尺寸是14英尺×8英尺。

The wave here has a length of 250 feet and a height of 10 feet. 这里的浪有250英尺宽10英尺高。

The house is more than twenty metres long and measures six metres in width. 这座房子长20多米，宽6米。

If a room is 3 metres wide by 3 metres long its area is 9 square metres. 如果一个房间是3米宽3米长，它的面积就是9平方米。

The floor is 3 metres wide by 5 metres long so its total area is 15 sq metres. 房间的地面是3米宽5米长，总面积是15平方米。

The box measures approximately 26 inches wide×25 inches deep×16 inches high. 这个箱子大约26英寸宽，25英寸深，16英寸高。

The area, measuring / which measures 5 kilometres by 3 kilometres, has been purchased by the army. 这个长5公里、宽3公里的区域已被军方购买下来。