Matcha on its own is one of the lowest calorie drinks in Japan. A bowl of usucha, whisked with water, is about 10 calories and 1g of tea. The latte is a different product. It is 300ml of full milk at 200 calories with a sweetened green tea powder stirred in, and the powder at most chains is roughly 40% sugar. You are drinking a small glass of milk with 2 teaspoons of sugar and a pinch of tea, and the colour makes it feel like a vegetable.
The sizes climb fast. Short is 170, tall 240, grande 320 and venti about 350. Whipped cream adds 80 to 100 on top. A venti matcha latte with whip is 450 calories, more than a bowl of kake udon, and it is a drink you have next to a meal, not instead of one. The konbini carton versions from Lawson and 7-Eleven are lighter at 120 to 150 for 240ml because they are thinner, but they are also sweeter per sip.
The lever is the milk, not the matcha. The same tall with non-fat milk is about 150 calories, soy milk about 200, oat about 210. Almond drops it to about 140. Sugar cannot be removed because it is inside the powder at most chains, but you can ask for one pump less of the syrup at shops that sweeten separately. Or drink the real thing. Hot matcha with water at a tea counter in Kyoto is 10 calories and tastes more of tea than any latte.