You can plug your info into online brew calculators (i.e. Grain types, wieght, brew house efficiency, temps, etc.) And see what your poss starting gravity was. Extract and all grain could have different results.
If this was an extract batch, your recipe's anticipated OG will be close enough to your actual OG, assuming you got the volumes correct. A known amount of extract dissolved in a known volume of water will yield a known gravity.
So...use your recipe OG and use the following formula: