In geometry, the elongated pentagonal rotunda is one of the Johnson solids (J<sub>21</sub>). As the name suggests, it can be constructed by elongating a pentagonal rotunda (J<sub>6</sub>) by attaching a decagonal prism to its base. It can also be seen as an elongated pentagonal orthobirotunda (J<sub>42</sub>) with one pentagonal rotunda removed.
The following formulae for volume and surface area can be used if all faces are regular, with edge length a:
The dual of the elongated pentagonal rotunda has 30 faces: 10 isosceles triangles, 10 rhombi, and 10 quadrilaterals.