Like other vegetables, most of the cucumber calories come from carbs. The cucumber’s weight is 95% water, and the rest is responsible for the cucumber calories.

Cucumber calories according to the USDA site:

• single large cucumber (8-1/4″, 300 gr) with peel – 45 calories
• single large cucumber (8-1/4″, 280 gr) peeled – 34 calories

You have to remember that although the number of cucumber calories for a peeled cucumber is lower than the number of cucumber calories for an unpeeled cucumber, that a lot of nutrients are inside the peel. So it is worth while to eat the cucumber and the peel and all of its cucumber calories.