If you don't have a scale, then do this format for measurement...
2cups water, 1/2cup DME
3cups water, 3/4 cup DME
You can use the 4-to-1 ratio to scale it to whatever size you need.
+1 on the scale, they are worth having for brewing, cooking, and other things. Just make sure it measures in grams and 1/10th of an ounce.