This is a question many people new to digital photography ask. How big can I print, well the answer may actually surprise you. Lets look at the current crop of digital cameras. The "smallest" megapixel (MP) cameras are in the 5MP range some are smaller but pretty tough to find. For example the Canon PowerShot A530 5MP Digital Camera. The image sensor is 2592 pixels wide by 1944 pixels tall. Generally accepted printing for images is 300dpi (dots per inch) in general we can think each pixel as a dot that will be printed so we take the 2592 divide that by 300 and we get 8.64 inches (about 22cm) and 1944 pixels will get us 6.48 inches (16.5cm). So this little guy right will produce nice prints for the typical person like a 4x6 or 5x7 that most people will print.
Can you print larger? Yes you can but you either have to invent the dots (interpolation) to upsize or use a lower DPI in order to print larger. One can safely drop down to 200 or even 150 dpi So we could get a 13x17 inch print out of this camera at 150dpi. Something this size would most likely be placed high and viewed from a further distance so the lower DPI would not affect quality of the print. If you were to get a few inches away you would notice it though.