Vacuum cleaner bags are made in standard sizes. Most bags of a particular size will fit vacuums of a particular style, regardless of what brand the vacuum is. For example, vacuum bags marked C are likely to fit most upright vacuums, whether the upright vacuum is Hoover, Eureka or something else. There are several size bags available for upright vacuums, while comparatively fewer available for other types of vacuums.
Although you can use a generic bag for any vacuum cleaner, it's usually best to purchase bags recommended by the manufacturer. Your particular brand of vacuum cleaner may have specific requirements that only the manufacturer recommended bags meet. Thus, your vacuum cleaner will probably run better if you use the brand-name vacuum cleaner bag than if you use a generic bag, and in some cases it may void your warranty if you use the wrong type of bag.
It's important to get the right size vacuum bag for your vacuum cleaner because the bag has to attach tightly to the cleaner to store dust and debris properly. If the bag is too big, it may not stay connected to the vacuum cleaner and if it's too small it may rip or tear. In either case, dust or dirt could get inside the vacuum and interfere with its functioning if you don't have the right size bag.
You can purchase vacuum cleaner bags at most stores that sell vacuum cleaners. In addition, you can visit the website for your vacuum cleaner brand to purchase new vacuum bags. If you can't find the right kind of bag because the manufacturer discontinued it, search online for overstock suppliers or check with vacuum repair shops. If you still can't find bags anywhere, call your vacuum cleaner manufacturer and ask if there are any other bags you can safely use.