Mathworld states a brief description of a diameter. It also gives a two-dimensional and three-dimensional diagram for a diameter.

WebMath offers a great site for students to practice finding the diameter, area and circumference of a circle.

A plan of the ground floor of the Capitol Building from 1825. The map is keyed to show: (A) House of Representatives, 96 feet radius; (B) Senate Chamber, 75 feet radius; (C) Central Rotunda, 96 feet in diameter; (D) Library, 92 x 34...

The 53 m high tomb built in ad 1006 for Qabus Ibn Voshmgir, Ziyarid ruler and literati, near the ruins of the ancient city of Jorjan in north-east Iran, bears testimony to the cultural exchange between Central Asian nomads and the...

The United States' largest cone-shaped burial mound, 62 feet (19 m) tall, 240 feet (73 m) diameter at base.

An image of "Window", created by Duccio Di Buoninsegna in 1288 (Stained-glass, diameter: 700 cm).

An image of "Desco da parto (recto)", created by Bartolomeo Di Fruosino in 1428 (Tempera on panel, diameter 59 cm).

An image of "Desco da parto (verso)", created by Bartolomeo Di Fruosino in 1428 (Tempera on panel, diameter 59 cm).

An image of "Leonello d'Este", created by Pisanello in 1444 (Bronze medal, diameter 6,7 cm).

An image of "Sigismondo Pandolfo Malatesta", created by Pisanello in 1445 (Cast lead, diameter 10 cm).

An image of "Medal of Cecilia Gonzaga (obverse and reverse)", created by Pisanello in 1447 (Bronze, diameter 8,7 cm).

An image of "Medal of Cecilia Gonzaga (reverse)", created by Pisanello in 1447 (Bronze, diameter 8,7 cm).

An image of "Cecilia Gonzaga", created by Pisanello in 1447 (Cast bronze, diameter 7 cm).

An image of "Alfonso of Aragon", created by Pisanello in 1449 (Gilded bronze, cast, diameter 11 cm).

An image of "Tempio Malatestiana", created by Matteo De Pasti in 1450 (Bronze, diameter 4 cm).

An image of "Self-Portrait", created by Jean Fouquet in 1450 (Enameled copper, diameter 8 cm).

An image of "Madonna with the Child and Scenes from the Life of St Anne", created by Fra Filippo Lippi in 1452 (Oil on panel, diameter 135 cm).

An image of "Madonna with the Child and Scenes from the Life of St Anne", created by Fra Filippo Lippi in 1452 (Oil on panel, diameter 135 cm).

An image of "Borso d'Este", created by Jacopo Lixignolo in 1460 (Cast bronze, diameter 8 cm).

An image of "Tondo Portrait of a Lady", created by Luca Della Robbia in 1465 (Glazed terracotta, diameter: 54 cm).

An image of "Frederick III, Holy Roman Emperor", created by Bertoldo Di Giovanni in 1469 (Copper alloy, diameter 6 cm).

An image of "Adoration of the Magi (from the predella of the Roverella Polyptych)", created by Cosme Tura in 1474 (Tempera on wood, diameter 38 cm).

An image of "Circumcision (from the predella of the Roverella Polyptych)", created by Cosme Tura in 1474 (Tempera on wood, diameter 38 cm).

An image of "Flight to Egypt (from the predella of the Roverella Polyptych)", created by Cosme Tura in 1474 (Tempera on wood, diameter 38 cm).