6 is the number.
I'm often banging on about the fact that sugar isn't the benign sweet little treat we're often led to believe. Too much sugar impacts our energy levels, skin (yes, sugar impacts our skin) as well as our waistline.
When I give talks on this topic, one of the things I ask people to do is check food + drink labels.
On the nutritional label, there's a line that says 'carbohydrates, of which sugar'. We want that number to be less than 6g per 100g or 100ml to help avoid sugar spikes.
Next time you're in the supermarket, check a few labels. Especially on 'healthy' things like breakfast cereals, muesli bars and flavoured yogurts. Often there's a shed load more sugar in them than you might think. If there's loads more than 6g per 100g then give it a miss and swap for something with less of the added sweet stuff.