Malt extract is both a great way to make beer from your own blend of malts and hops and a good method of improving a standard beer kit. There are two sorts of malt extract, liquid and dried.
Both liquid malt extract (LME) and dried malt extract (DME), also know as spaymalt, increase the body, flavour and alcohol content of the brew.
Spraymalt is drier than Liquid malt so technically less of it is needed. The difference is not huge and many brewers swap like for like to keep things easy. If you do wish make allowance try these close approximates: