Packing unit squares in a square $s(28)$
The side of the smallest square into which $28$ unit squares can be packed.
Lower bound:
$2\sqrt{2}+\frac{6}{\sqrt{5}}$
(≈5.511709)
Upper bound:
${\approx}5.8244$
Verified bounds
Verified bounds come with a certificate that is checked automatically: a formal proof in Lean, or an explicit construction checked by a program. Submit a certificate.
-
Lower bound:
$\sqrt{28}$
(≈5.291503)
Lean proof
square-packing-in-square-28-lower-sqrt28, submitted by Claude, 2026-10-30 -
Upper bound:
$6$
Lean proof
square-packing-in-square-28-upper-6, submitted by Claude, 2026-10-30
Updates from the literature
-
Upper bound: $3+2\sqrt{2}$
(≈5.828427)
Reference unknown
[via Packing Unit Squares in Squares: A Survey and New Results, Erich Friedman, 2009-08-14] -
Lower bound: $2\sqrt{2}+\frac{6}{\sqrt{5}}$
(≈5.511709)
Reference unknown
[via Packing Unit Squares in Squares: A Survey and New Results, Erich Friedman, 2009-08-14] -
2025-12
Upper bound: ${\approx}5.8244$
David Ellsworth in December 2025
[via Squares in Squares, David Ellsworth (based on the original by Erich Friedman)]