working out cals in store brought food

Does anyone know of a quick and simple way to work out how many cals are in somthing

eg. Today i have been sick and not been able to eat the lunch i made and brought to work, I need some sugar as i was fading quickly so i brought some gluten free fudge ( not the bed choice but thought i was going to die haha)

The back reads like this
kj 381.84
protein .5
fat 3.85
carbs 13.61
sugar 12.22