Grinding coffee beans in the blender is possible, but not recommended. It is not recommended for two basic reasons. First, the granules produced from blender-ground coffee beans will be inconsistent sizes. A consistent grind directly affects the flavor and caffeine extraction. The second reason is that coffee beans will wear down the blades of the blender very quickly.
For people who have to use a blender, they need to chop the coffee beans into smaller pieces first. They can use a mortar and pestle to gently crack the beans or to put them in a heavy duty plastic bag and smash them with a rolling pin or another heavy, blunt object. Once the beans are slightly broken down, the blender will have a better chance of grinding the beans to a usable size. Next they add the pre-chopped beans to the blender a handful at a time. The grind setting, for blenders that have it, is best for this. They then can add more handfuls of beans to the blender once the first batch is appropriately sized. It's important for the blender lid to be secure before adding beans to the blender. Glass blenders are the only suitable blenders for this — not plastic.
Although it is possible to make the blender method work in a pinch, there are several options that people might explore first. The most obvious choice for people to buy a coffee grinder. Many brands are available for less than $50. Second, someone in a bind can ask a friend or neighbor if they can use their grinder. Third, a local coffee shop might be willing to grind the beans, especially if the beans were purchased at one of their locations. Most grocery stores also have a coffee grinder in the coffee aisle that shoppers are welcome to use for free. For shoppers who have a bag of whole beans at home, the best option is to ask to the customer service desk if it is acceptable for to use the store’s grinder.