I don't really get some of the semi-insulting replies this guy's getting. Talking about kilojoules is "overthinking" it??? You know that's just a measure of energy, the same as kilocalorie, or calorie, right?
The guy is a rank beginner simply trying to figure out how many calories he should eat to grow based on the common model of "maintenance + surplus."
I realize a lot of people don't like to count calories at all, but it can be helpful especially for a beginner who really has no idea what he ought to be doing. I know it helped me!
To the op, depending on your size here's what I would do. Pick a round number like 3000, 3500, or 4000 and try to develop a diet that hits that number. Since it sounds like you're pretty small, I would probably start with 3000 (that's kilocalories). Find a diet that works for you that hits 3000 kcal, and stick to it for a couple weeks. Note how fast you're gaining / not gaining weight (weigh yourself a couple times a week or every week or two, doesn't really matter) and make adjustments based on that.
When I first learned how to eat, I heard someone throw out the number 4000-4500. I didn't question it; I didn't ask why; I just looked at a list of foods that were good to eat, and made a diet plan incorporating them that hit those numbers day in and day out. It worked great for me, and I gained 25 lbs in 3 months, the vast majority being muscle. Unfortunately I had to go back to frat food after that for 9 months...
For a good list of foods to eat, you can check out the "Bodybuilding Bible" thread that's linked inside the "Best of T-Nation" sticky at the top.