More than three quarters of the sites I’ve checked say that the white of an extra large egg has 17 calories. Another one says 35. Yet another says 20. I’m thinking closer to 17 because it’s such a common answer and 35 seems like an anomaly. Who knows?
This sez 17 calories in a large (33 g) egg, or 52 calories per 100 g.
(If you’re SERIOUS about calorie counting, this is the best and easiest calorie calculator I’ve found.)