Well, you could try using an IV calculator. You should be able to find some by using a search engine such as Google. However, since some IV calculators slightly disagree with one another, I am loathe to post a link and thereby risk giving a site whose calculator may not quite be accurate. I suggest you look on your own and find one that seems right to you.

Note that battling may skew the results, as your Pokemon could gain EVs in the process. For best results with trained Pokemon, you should probably use some of the berries which lower IVs. (On the berry's description, it should say that it "lowers base _____.") When you cannot use any more of those berries, it means that the given stat has been drained of all EVs. This means that you'll have to re-earn your EVs, but it can actually be very helpful, as you can carefully plan your EV distribution after you have access to more areas later in the game.

Another option is to talk to one of the old men in the Battle Frontier. I can't remember exactly where he is, but one of the men will be able to tell you how good your Pokemon is and what its best stats are. However, this will only give you a general feel for your Pokemon's strengths and weaknesses; it doesn't give you exact figures for anything. Still, it can be easier than an IV calculator, as you don't have to search online for it, and you don't have to drain your Pokemon's EVs to get an accurate assessment, either.