# What is the smallest convex set includes all smooth unit curves?

I try to understand: is there a smallest in area convex set that every smooth curve with length 1 can be placed inside it by translation and rotation?

I only have a upper bound $S \leq \frac14+\frac{\pi}{16}$ because of convex hull of two circles radius $\frac14$ and simple lower bound $S\geq\frac1{4\pi}$.

Does this set exist and what is its length?

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Is your question the same as this one on MathOverflow? Smallest area shape that covers all unit length curve – Rahul Dec 24 '11 at 3:19
Oh, I've searched here, not on the MathOverflow because this problem looks so pretty simple. Thx. – sas Dec 24 '11 at 4:33

They credit the smallest cover yet discovered to Gerriets & Poole (in 1973 or 1974), and describe it as a "certain truncated rhombus of area less than $0.286$...". Maybe someone will have a link or reference to the particular shape? For your bounds, I would only point out that the convex hull of a semicircle of arclength $1$, with radius $1/\pi$ and area $1/(2\pi)$, gives a better lower bound (of $0.159...$).