I keep this handy-dandy Conversions and Equivalents chart bookmarked:
http://www.realfood4realpeople.com/convert.html
It even includes ingredients substitutions, and differing names and values, such as creams, chocolate, etc.
About Splenda (sucralose sweetener), as Rachel pointed out, it comes as a bulk powder which you can measure out just like regular sugar -- it has maltodextrin as the "filler". 0.5 gm of the product sweetens as 1 tsp (5 ml) of regular sugar, and provides 0.5 gm carb/2 calories. Here in N. America we can also buy Splenda in little paper packets; these are handy to carry in the purse, and restaurants provide these as well. This type of Splenda has dextrose mixed with maltodextrin as the filler ... each little packet sweetens equivalent to 2 tsp (10 ml) of regular sugar, and weighs 1 gm (note, it is more concentrated than the bulk type, so there is only 1/4 tsp powder in the packet). Anyway, each packet has 1 gm carbs/ 4 calories.
So, there is no difference in carbs or calories between the bulk type or the concentrated powder in the little packets for the equivalent amount of "sweetening power". Or in weight, for that matter.
100 gm of Splenda, either type ... would provide 100 gm carbs and 400 calories ..
Apparently, there's a zero-carb LIQUID Splenda available in some corners of the world, but not yet in Canada, UK or USA.
Stevia is a natural plant extracted sweetener, that has zero carbs. It has a slight licorice/anise flavour that not everyone likes, but it is available in health food shops in the UK.
Hope this helps
Doreen