Rashi on Exodus 26:16/רש"י על שמות כ״ו:ט״ז

1עשר אמות ארך הקדש TEN CUBITS SHALL BE THE LENGTH OF A BOARD — This tells us that the height of the Tabernacle was ten cubits (since the boards were standing vertically).

2ואמה וחצי האמה רחב AND A CUBIT AND A HALF SHALL BE THE BREADTH — This teaches us that the length of the Tabernacle corresponding to the twenty boards which were on the north and on the south was 30 cubits from east to west.