Cincau is genuinely one of the better drink options you can order at the mamak or the roadside stall. 80 calories for a full glass, and the grass jelly has practically nothing in it, around 20 calories for 100g. The jelly is basically a free food. The entire calorie count comes from 45g of sugar syrup which adds 55 calories. So if you are cutting, this is a solid choice compared to teh tarik or Milo ais which can hit 150 to 200 calories easily.
The real thing that changes the number is how heavy-handed the uncle is with the syrup. Some stalls just dump it in. Always ask for kurang manis lah, it is not a weird request and it drops you from 80 to about 50 calories. The soya cincau version (what people call Michael Jackson) replaces the water with soya milk, so you get a bit of protein out of it but also about 60 to 70 extra calories, landing around 140 total. Still not bad for a drink. The versions to avoid are anything with condensed milk drizzled over it.