Photo quality in a final print is 200 pixels per inch (the "300dpi" figure that you hear sometimes relates to commercial printing presses and isn’t meaningful for digital cameras and digital lab printers). That said, 200 pixels per inch is no guarantee of high quality. The 10-megapixel point and shoot camera may have low contrast and sharpness from the cheap lens plus high noise in shadow areas from the small sensor. You would probably get a better print from an old 6-megapixel digital SLR.

• 2000×3000 pixels (6 megapixels); good for prints up to 10×15" in size
• 2700×3600 pixels (10 megapixels, average digital SLR); good for prints up to 13×18" in size
• 2900×4400 pixels (13 megapixels, Canon 5D); good for prints up to 15×22" in size
• 3300×5000 pixels (16.6 megapixels, Canon 1 Ds Mark II); prints up to 17×25"
• 4080×5440 pixels (22 megapixels; medium format backs); prints to 20×27"
• 5400×7200 pixels (39 megapixels; medium format backs); prints to 27×36"
• 10000×14000 pixels (140 megapixels; large format scanning backs); prints to 50×70"

Note that the "print size" is the maximum at which you’ll get the kind of print quality that one would have gotten with the best film equipment, enlarged no more than about 10x. By this standard, the largest that you could have enlarged the typical 35mm negative before a noticeable reduction in quality would be 10×15", the same as the 6-megapixel digital SLRs. A 6×7cm medium format negative at 10x will enlarge to 24×28". A 4×5" sheet of film could enlarge to 40×50" and withstand close inspection.

http://www.learndigitalphotographynow.com/