Brompton gearing and chain length

[Gattopardo]

My brompton has a 3 speed Sturmey archer hub and was geared to 50 13.  The replacement crank is a 54. 

What rear cog would I need to keep the gearing similar and then the chain length.  Currently I have a 13, 14 and 15 toothed rear cog.

[Diver300]

54 - 14 is almost exactly the same gearing as 50 - 13

[PaulF]

Unfortunately you can't have both the same gearing and the same chain length.

14.04T but they're pretty rare to keep the same gearing so obviously the 14T or a 9T to keep the same chain length but they're even rarer.

[Gattopardo]

This just confused me more will 102 be too long and 100 too short?

Also am running a 1/8th chain with a connector.

[Pickled Onion]

102L will be absolutely fine with 54x14 (if that's what you're asking) since the table shows it will accommodate a two speed 54x12 - 54x16