Dimensions and characteristics
The dome's springing point stands 177 feet above ground level, while its height from the drum base to the top is about 108 feet. The distance between two opposite edges of the exterior octagonal base is about 176 feet. The height of the lantern atop the dome is slightly more than 72 feet. The dome weighs an estimated 37,000 metric tons, and the number of bricks used in the structure may exceed four million.
The vertical ribs of the dome display a "pointed fifth" curvature, i.e., the dome's radius is equal to four-fifths of the base diameter. The resulting elevation is far greater than that of a "round" dome, i.e., one whose radius is equal to the radius of the base circumference.
A self-sustaining design
Brunelleschi built the dome without the use of a wooden centering. He adopted the "herring-bone" technique to ensure the stability of the brickwork courses, whose inward slope increases continually from the base to the dome's closing stone ring. Each successive ring of bricks tightens the structure, keeping it continuously in equilibrium.