Tarski's circle-squaring problem is the challenge, posed by in 1925, to take a in the plane, cut it into finitely many pieces, and reassemble the pieces so as to get a of equal. This was proven to be possible by in 1990; the decomposition makes heavy use of the and is therefore. Laczkovich estimated the number of pieces in his decomposition at roughly 10 50. More recently, in 2017, Andrew Marks and Spencer Unger gave a completely constructive solution using. In particular, it is impossible to dissect a circle and make a square using pieces that could be cut with an pair of scissors (that is, having boundary). The pieces used in Laczkovich's proof are.

Laczkovich actually proved the reassembly can be done using translations only; rotations are not required. Along the way, he also proved that any simple in the plane can be decomposed into finitely many pieces and reassembled using translations only to form a square of equal area. The is a related but much simpler result: it states that one can accomplish such a decomposition of a simple polygon with finitely many polygonal pieces if both translations and rotations are allowed for the reassembly. It follows from a result of that it is possible to choose the pieces in such a way that they can be moved continuously while remaining disjoint to yield the square. Moreover, this stronger statement can be proved as well to be accomplished by means of translations only. These results should be compared with the much more in three dimensions provided by the; those decompositions can even change the of a set. However, in the plane, a decomposition into finitely many pieces must preserve the sum of the of the pieces, and therefore cannot change the total area of a set ().

Tarski's circle-squaring problem is the challenge, posed by Alfred Tarski in 1925, to take a disc in the plane, cut it into finitely many pieces, and reassemble the pieces so as to get a square of equal area.

See also [ ] •, a different problem: the task (which has been proven to be impossible) of constructing, for a given circle, a square of equal area with alone. References [ ].