If you built the recipe in beersmith or similar program it should give you an estimate, that should be pretty close. You can also calculate it, especially with honey which is 100% fermentable. I don't know off hand what honey is in points per pound per gallon, but for example, if it's 45 PPG and you used 5 pounds of honey in five gallons, your OG will be 1.045. (45 points/lb * 5 lb) / 5 gallon (the 5's cancel).