A number must be centred on the back of each shirt. Only whole numbers may be used, no number higher than 99 may be used and the number 1 may only be used by a goalkeeper.
Numbers must be of a single colour that contrasts with the number zone in accordance with.
Numbers must be clearly legible. The stroke width of each digit must be 2–5cm and the digits themselves must be:
25–35cm high on men’s shirts;
20–35cm high on women’s shirts.
Numbers must be clearly legible to the referee team, commentators, spectators and TV viewers, in daylight and under floodlights, from at least 50m away.
Numbers must also appear on the front of shorts, on either leg and in any position. Short numbers must be between 10cm and 15cm high, be clearly legible and clearly contrast with the colour of the shorts.
Numbers may contain a team emblem (or part thereof) of no more than 5cm² in the bottom of each digit.
Numbers must be free of manufacturer identification, sponsor advertising and decorative elements.
Numbers may contain breathing holes or lines up to 2mm wide and they may be divided into up to four parts, provided the divisions do not exceed 2mm.
For the sake of legibility, digits may be surrounded by a shadow outline, 3D effect or contrasting key line of a decorative colour. Key lines may be around the outside of the number or just inside. Shadow outlines, 3D effects or contrasting key lines are however not taken into account when measuring number height.
Numbers may also be placed on the front of shirts for representative team competitions, and they may be mandatory under certain competition regulations. Numbers on the front of shirts must be between 10cm and 15cm high, be clearly legible and clearly contrast with the colour(s) of the shirt.