There are approximately 173 calories in a slice of cinnamon toast.
You can make a very basic cinnamon toast using shop bought bread and sprinkling with ground cinnamon and sugar. This way you can calculate the calories quite easily by looking at the nutrional information on the bread and adding a little extra for sugar etc. You can of course use wholemeal or light bread for a healthy option too.
However, cinnamon toast is the sort of recipe that can be personalised, and obviously it depends which recipe you use and what ingredients it contains as to how many calories there are per slice.
For example, if you add raisins, walnuts or chocolate as some recipes suggest, you will of course be increasing the calories, as will spreading with butter rather than a low fat spread.