Okay, first off, equity is not just how much you've paid down the loan. That's part of it, but the way I would calculate it is the value of your house (go online, look at some recent sales in the area that are similar to your home in size, # bedrooms, etc. - or you could even contact a Realtor who will do it for free, I do them all the time), subtract about 10% off of that to account for any realtor/closing costs, and then take THAT value and subtract the amount left on your loan. That's your equity. No more "guessing".
You need to know the value of your house and how much it would rent for. Don't fall into the classic trap of "oh I'll just rent it out and make some extra money." DO THE MATH. Look at what it costs to maintain the house (including a repair reserve for emergency repairs), vacancy, property manager if you'll use one, PLUS taxes, insurance, principle and interest payments. Will the rent coming in each month cover all those and give you a little extra? If the answer no, then don't rent it out. Just sell it and move to a bigger house when you are ready.
I'm telling you this because I see people make this mistake all. the. time. Primary residences typically do NOT make good rentals unless you bought them with the end goal of turning them into a rental in mind. Primary residences are bought because of their features, and emotions associated, not because the math works out.
Post all the #s of your primary residence in the Real Estate forum and we'll tell you if it'll make a good rental or not.
I just don't want to see you buy another house thinking your first one is now an 'investment' because you have decided to call it one, and then being responsible for TWO houses and not able to keep up with either.
Sorry if that was harsh.
Edit to add: basically everything SwordGuy says ^^.
