How to convert Grain wieght into extract weight?

I went to the library and got a great recipe book, since I live in Alaska shipping is about 1/4 of the price of my brewing shopping list. So if a recipe asks for say 6lb of a certain grain. What would DME or LME be the equivalent of it be. Should I not deffer from the recipe or can Extracts be subtituted?

A rough estimate is multiply the base grain by .75 for LME and .6 for DME. This is assuming your recipe uses a basic malt like 2-row. If it uses a combination of base malts like 2-row and munich then the grain to extract substitution is difficult. In addition you may need to add specialty grains. Software like beersmith has a built-in converter so if you enter the all grain recipe it will convert to extract for you.

Liquid Extract = .75 x Base #
Dry Extract = .6 x Base #

according to those number 6lb of grains would equal 3.6lb of DME wich would make shipping cost way less. Thanks