The dwarf planet Ceres is on average 2.77 AU from the Sun.

Kepler's laws. Orbits are ellipses with the Sun at a focus. The line to the Sun sweeps equal areas in equal times, so at the nearest and farthest points $v_1r_1 = v_2r_2$. And $T^2 \propto a^3$: for bodies around the Sun, $T^2 = a^3$ with $T$ in years and $a$ in AU.