It is very difficult to measure memory in cats because there's a lack of studies on felince cognition. That, combined with their semi-domestication, makes them much more difficult to train than dogs.
Live Science says "Within the cerebral cortex — the brain region responsible for information processing, problem-solving and perception, among other things — cats have 300 million neurons, compared with dogs' 160 million neurons."
Cats' (versus dogs') memories are "almost 200 times more retentive. Without repeated reinforcement training, a dog's memory span is about 5 minutes. Cats, on the other hand, averaged about 16 hours, only if the activity benefited them."
We often hear stories about dogs being reunited with their owners after several years absence and them remembering them and being excited to see them. We don't think of that happening with cats but read this interesting story about a cat reunion that happend at Noah's Ark Animal Hospital in Danbury, Connecticut - Click here.