How many A Levels is Foundation Diploma in Art & Design equivalent to?

I know it's recognised as equivalent to A Levels, but how many for the Pass, Merit and Distinction grades?

That depends whether you're taking a normal or extended FAD and also whether it's a BTEC or a UAL accredited course.

For a BTEC course https://www.ucas.com/ucas/undergraduate/getting-started/entry-requirements/tariff/tariff-tables/1246 a distinction is worth a smidge of BBC at A level, a pass roughly DDE.

For UAL courses https://www.ucas.com/ucas/undergraduate/getting-started/entry-requirements/tariff/tariff-tables/1006 the extended diploma is worth around ABBB at distinction and DDD at pass. The standard diploma is worth roughly BB at distinction and DE at pass.

For the standard diploma you usually have to have A levels as well so your total tariff will be higher. The Extended diploma is designed as an A level equivalent (so you can start it straight after GCSE) and takes 2 years.