The size of the memory card used in a specific digital camera does not affect the performance of the camera, but it is dependant entirely on your need for space for being able to save the number of pictures you want to.

When you are planning to purchase the memory card, always consider factors like your requirement in terms of the number of photographs you want to take and save on the card. If you are fond of traveling across the world, your need will vary in comparison to an individual who needs the camera only for vacations. Another factor to be considered would be the file size. If you want to take pictures which need to be printed, they will occupy more space in comparison to the ones which are clicked to be uploaded online.

128MB memory card is well sufficient for a camera with two mega pixels, whereas in case of cameras with three or four mega pixels, you can choose memory cards between 128MB and 256MB based on your need. But in case you possess a digital camera with five mega pixels, it is recommended to choose memory cards which have 256MB of storage space.

Below are tentative figures about the approximate number of images a flash memory card can store:
128MB: This size of storage space is sufficient for 21 to 41 uncompressed and large pictures or up to 100 compressed photos, and is suitable for most photographers.
256MB: This size of storage space is sufficient for 42 to 82 uncompressed and large pictures or up to 200 compressed photos, and is suitable for use in wedding ceremonies and events where you want to capture most of the treasured moments.
1GB: These are most suited for people who plan to spend a lot of time in clicking pictures during their vacations. The space is almost four times of the 256MB card and is sufficient for 168 to 328 uncompressed and large pictures or up to 800 compressed photos.

You can choose any of these memory cards based on your needs and can even consider carrying several small sized memory cards which can be conveniently replaced when the complete space is occupied. It’s a simple procedure and this is a good option if you possess a small memory card beforehand.