What is width and length of one third of an acre?

First of all, why do you assume that the acre is rectangular? An acre can be circular of octagonal or a completely irregular shape.

Next, even if you are told that the shape is rectangular, there is no way to distinguish between a near-square shape and a long thin shape.

One third of an acre = 14520 sq ft.

So it could be

120 ft x 121 ft

or 1 foot x 14520 ft or 1 ft * 2.75 miles

or 1 inch x 174242 ft or 1 inch x 33 miles

etc