Measuring your own is the simplest/surest way.
Hosetechniques.com sells 'em for good prices.
You do realise that you will have to Zip tie the Hoses on?? they tend to pop off if not.
Although in Fairness there is NO genuine advantage over OEM.. besides pretty colours
For the small vacuum lines which are the main ones to replace, I think the rubber hoses are 3mm ID, but for silicone you can use 2mm or 3mm ID. I think 2mm is better as it's a tighter fit and as Basre says, silicone hoses are more prone to popping off or leaking unless tied.
Agreed though that the best and surest way is to measure yourself :cheesy:
Be careful with the hose to the MAP sensor from the inlet manifold - I don't advise replacing this unless it's rotten, as its characteristics are critical to the correct running of the engine. If you do replace it, I think it's safest to get a genuine item.