Buying whole flax seeds can be cheaper than buying them pre-ground and grinding is easy to do.  Use a blender, food processor, or designated coffee grinder.  Add whole flaxseeds to your blender or food processor and blend until they break down in size and become a powdery substance.   If you’re using a blender, large batches do better in large pitchers.  If you’re using a coffee grinder, it’s best to use one that’s not used for coffee, otherwise, it may alter the flavor of the flax seeds.  Stop scraping down the sides, grinding the whole flaxseeds shouldn’t take long.   Usually, pre-ground has a finer texture than grinding your own. Store them in an airtight container in the refrigerator.  How long they last in the fridge will vary, so I only do what I’ll use in 1-2 weeks.