Looking to convert an all grain recipe to malt extract or vice versa? This can be done with some calculations. The main goal in converting recipes is to keep the gravity and bitterness level the same, regardless of your type of ingredient. Dry malt extract, liquid extract, and malted grain all contribute similar sugars and gravity points to beer, but in different amounts.
Dry malt extract usually contributes 45 gravity points per pound per gallon. This means that one pound of dry extract in one gallon with have a gravity of 1.045. Likewise, liquid extract will add 36 points per pound per gallon. Grain malt is more complex as each grain will add a slightly different contribution, and brewhouse efficiency in extracting sugars from the mash also affects the calculation; as a rule of thumb, you can figure that base malt and caramel/crystal malts will add 26 points per pound per gallon.
If, as an example, you have an all grain recipe with a 1.050 original gravity and it calls for 9 pounds of Pilsner malt, you could brew the extract version of that recipe by either using 7 pounds of liquid pilsner extract or 5.5 pounds of dry pilsner extract. Any of those recipes would give you a similar beer with a 1.050 original gravity.
If you are converting from a partial volume boil to a full volume boil (or vice versa), there may be some changes in hop utilization. This means that you may have to slightly increase or decrease the amount of bittering hops you are using, depending on wort gravity and volume of the boil. The easiest way to check on these amounts and to precisely calculate grain to extract conversions is to use a brewing calculator.