the new notes are around 15% smaller than the current paper notes but will retain the traditional look of the existing notes, with a portrait of Her Majesty the Queen on the front and historic characters on the back. The new banknotes include symbols representing all four of the home nations, with imagery taken from the Royal Coat of Arms and the Royal Badge of Wales.
What size will the new banknotes be?
The polymer £5 note is 125mm x 65mm (the current paper note is 135mm x 70mm).
The polymer £10 note will be 132mm x 69mm (the current paper note is 142mm x 75mm).
The polymer £20 note will be 139mm x 73mm (the current paper note is 149mm x 80mm).
The existing format of tiered sizing will be maintained, i.e. the higher the denomination, the longer the height and the length of note.
http://www.bankofengland.co.uk/banknotes/polymer/Documents/QALibrary.pdf