Thanks a lotI'm assuming you are asking in context of PPR/RFV. Use what the RFV email/PPR letter says so.
Mine said:
- 50 mm x 70 mm (2 inches wide x 2 3/4 inches long) and sized so the height of the face measures between 31 mm and 36 mm (1 1/4 inches and 1 7/16 inches) from chin to crown of head (natural top of head)
And, hence I used 50 mm x 70 mm.