It's 3.5 WITH filter, 3.0 WITHOUT (6.0 and 5.3 pints respectively) as said, never fill it right up to the max I always go just below the max level on mine, IIRC the difference between the low mark and the high mark is around 1 litre. I still have my 5 litre can from when i changed mine and have used it for top ups ever since, it's only just empty now.

Martin