Not really, there's a standard size depending on how large a battle it is- between 1500-2500 pts (which is what most battles are) it's usually a 6'x4' table. Other than that common dimension there's not a universally used surface limitation.
Yeah, it's as baron spikey says. If you read up on P88, the game is designed to be played on a 4x6 surface, but you can have any size if you want. Some people play on a 4x4 surface for small games, or 6x8 for really large, apocalypse size games.
Just remember that changing the board size too much can have an impact on game balance - large boards tend to help fast or shooty armies, small boards help slower or assault armies. It's usually not a huge difference, but it's something to keep in mind.
You'll usually find all tournament games are on 6x4 tables.
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