What is a rhombus?

A rhombus is a four-sided shape with all four sides the same length. Opposite sides are parallel and opposite angles are equal, so every rhombus is also a parallelogram. Its diagonals cross at right angles and cut each other in half. A square is a rhombus with four right angles. Children often call a rhombus standing on a corner a diamond, but diamond is not a mathematical name.

Examples

• A shape with four 5 cm sides and angles of 60° and 120° is a rhombus.
• A square is a rhombus with right angles.
• Area of a rhombus: half the product of its diagonals, or base times height.

Quick facts

• Every rhombus is a parallelogram and a kite, but only a rhombus with right angles is a square.
• The diagonals of a rhombus cross at 90° and bisect each other.
• The plural is rhombuses or rhombi; both are accepted.