The playing field
The field of play is between 130m and 145m long and 80m to 90m wide. The dimensions may be reduced for underage games or games of less than 15 a side.
Line markings
All lines are marked in white. The lines on the playing field are 90mm ± 13mm.
Lines are marked across the field parallel to the endline at distances from each endline of 13m, 20m and 45m. The intersection of these lines and of the endlines with the side lines are marked with flags or cones. If flags are used, they set back at least one metre from the sideline and placed on an angle.
The midline of the field is marked parallel to the endlines and is 10m long. Boundary lines are part of the field of play.
Two rectangles are formed in front of the scoring space as follows: 
- One rectangle, 14m by 4.5m is formed by two lines 4.5m long and at right angles to the endline, marked 3.75m from the inside of each goal post and the ends of the lines are joined.
- A second rectangle 19.5m by 13m is formed by two lines 13m long at right angles to the endlines, marked 6.25m from the inside of each goal post and the ends of the lines are joined.
- The endline, including the goal line is part of each rectangle. The other three lines enclose the area of that rectangle.
A semi‑circular arc of 13m radius, centred on the midpoint of the 20m line is marked outside of each 20m line. A point is marked 11m from the centre of the goal line, where a penalty kick is taken.
Interchange/substitution zone
An area of the sideline extending 5m on either side of the centre line is marked as the Interchange/Substitution Zone and all players coming off/going on to the field of play in acts of interchange/substitution/temporary substitution go through this point.
Goals
The scoring space is at the centre of each endline. Each is formed by two goalposts, circular in cross section, and are not less than 7m high and are 6.5m apart.
The inside edge of the endline is at a tangent to the front edge of the base of the goal posts.
A cross is fixed to the goalposts 2.5m above the ground. The crossbar has a rectangular or circular cross section.
If rectangular, the depth is 140mm + 10mm and the width not less than 50mm. When circular, it has a uniform diameter of 125mm + 5mm.
Goal nets are securely fixed to the back of the crossbar and the back of each goal post.
References
Gaelic Athletic Association (Established 1884) Official Guide - Part 2. Central Council of Association, Croke Park, Dublin 3. April 2016.
https://learning.gaa.ie/sites/default/files/2016%20Official%20Guide%20-%20Part%202.pdf
Sport association details