Matched: the best known value
Packing 28 unit squares in a square
What is the smallest square that holds 28 squares of side 1, without overlap? The best known answer is a side of 5.8244446167, from David Ellsworth, 2025. Velmar Cut matched it.
The numbers
| Best known side | 5.8244446167 |
|---|---|
| Best known side, in full | 5.82444461667405 |
| Side from Velmar Cut | 5.8244446167 |
| Side from Velmar Cut, in full | 5.824444616675155 |
| Difference, Velmar Cut minus best known | +1.105E-12 |
| Found by | David Ellsworth, 2025 |
| Status | Best known, not proved |
| Time to reach it | 3238.437 s in all, several runs |
| Threads used | 4 or more |
| Machine | Intel Core i5-12600K, 10 cores, 16 threads |
| Squares | 16 upright, 12 turned |
| A plain grid needs | side 6 |
The time to reach this result on one desktop PC.
The problem at 28 squares
Three squares more than a grid of side 5 holds, so a plain grid needs side 6. The source table gives the best known side as a root of a polynomial of degree 6, about 0.004 below the 3 + 2√2 known since 1979. This layout has sixteen upright squares and twelve turned.
A plain grid: side 6
Best known: side 5.8244446167
Blue squares stand upright, orange squares are turned. Both pictures are at the same scale.
History
The best known value at this size is the result of David Ellsworth, 2025, and it is their result that Velmar Cut equals.
Best known, not proved: in Friedman's 2009 survey the best lower bound was 5.5117 (Trevor Green), so a smaller square has not been ruled out.
David Ellsworth's packing of December 2025 is rigid. It improved on the value Frits Göbel found in early 1979, which Erich Friedman's 2009 survey still gives as the best known.
| When | Side | Who | What happened |
|---|---|---|---|
| early 1979 | 3 + 2√2 ≈ 5.82843 | Frits Göbel | found |
| June 2023 | same side | David Ellsworth | semi-rigid alternative with the fewest turned squares |
| December 2025 | ≈ 5.82444 | David Ellsworth | improved, best known today, rigid |
Sources
The best known values come from "Squares in Squares", David Ellsworth, from the original by Erich Friedman.
Each size names who holds its value and since when. It is their result that Velmar Cut equals.
Is the packing valid?
Yes. The certificate passes the exact check: 28 pieces, each exactly a unit square, each inside the box, no two overlapping.
How close is it to the best known value?
The side from Velmar Cut minus the best known value is +1.105E-12, within the rule's 1E-11.
A match: the certificate passes the exact check, and |L - best known| <= 1E-11, the difference published unrounded for each size. L is the side of the certificate's box, rounded up at 15 decimals.
Downloads
The sides in the CSV are in units of one square's side. DXF and DWG are in millimetres, with squares of 100 mm.
You don't have to trust us
With plain Python and no other software, verify_exact.py beside the certificate checks the file above by exact arithmetic, with no rounding.
python verify_exact.py 28-squares-in-a-square.csv --squares=28 --reference=5.82444461667405 --epsilon=1e-11It does not prove that the packing is optimal, that the reference is the current best known value, or how the layout was found.
Free trial
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