What is the length of an A380 aileron?
A good source of public information is the aircraft characteristics document that the manufacturers typically publish for each model, including the A380.

A scale planform drawing can be found on page 310 of the PDF, subject 8-0-0. Based on this drawing, the rough size of the ailerons can be estimated.

The aileron is divided into three sections which move independently (see Why do some aircraft have multiple ailerons per wing?). The outboard section is about 4m (13 ft) long, the middle section is about 3m (10 ft) long, and the inboard section is about 2m (6.5 ft) long. In total they are about 9m (29.5 ft) long.

Derived from Airbus document:



Ailerons viewed from cabin:


Image source (other question)