Jamieson, Fausset and Brown on 2 Chronicles 3:3

3. these are the things wherein Solomon was instructed for the building of the house of God--by the written plan and specifications given him by his father. The measurements are reckoned by cubits, "after the first measure," that is, the old Mosaic standard. But there is great difference of opinion about this, some making the cubit eighteen, others twenty-one inches. The temple, which embodied in more solid and durable materials the ground-form of the tabernacle (only being twice as large), was a rectangular building, seventy cubits long from east to west, and twenty cubits wide from north to south.