Printing Images- what file size do you need

From: 
http://www.urban75.org/photos/print.html

Printing images - what file size do you need? A guide to required file sizes for printing out photos [Updated Feb 2016]
Image size Pixels (Virtual Size of Scans)	Megapixel rating	Print size (inches) at 200ppi	Print size (inches) at 300ppi
640  x  480	0.3	3.2 x 2.4	2.1 x 1.6
1,024 x 768	0.8	5.1 x 3.8	3.4 x 2.5
1,280 x  960	1.2	6.4 x 4.8	4.2 x 3.2
1,504 x 1,000	1.5	7.5 x 5.0	5.0 x 3.3
1,632 x 1,224	2.0	3.3 x 6.1	5.4 x 4.1
2,000 x 1,312	2.6	10.0 x 6.6	6.7 x 4.4
2,240 x 1,488	3.3	11.2 x 7.4	7.5 x 5.0
2,275 x 1,520	3.5	11.4 x 7.6	7.6 x 5.1
2,272 x 1,704	3.9	11.4 x 8.5	7.6 x 5.7
2,590 x 1,920	5.0	13.0 x 9.6	8.6 x 6.4
3,008 x 2,000	6.0	15.0 x 10.0	10.0 x 6.7
4,256 x 2,848	12.1	21.3 x 14.2	14.2 x 9.5
4,536 x 3,024	13.7	22.7 x 15.1	15.1 x 10.1
5,782 x 3,946	22.8	28.9 x 19.7	19.3 x 13.2
Professional/online printing Some professional services specify lower resolutions for image sizes, so you could get away with smaller image sizes. Kodak, for example, suggests these resolution/file sizes: For a 4" x 6" print, the image resolution should be 640 x 480 pixels minimum. For a 5" x 7" print, the image resolution should be 1024 x 768 pixels minimum. For an 8" x 10" print, the image resolution should be 1536 x 1024 pixels minimum. For a 16" x 20" print, the image resolution should be 1600 x 1200 pixels minimum. For a 20" x 30" print, the image resolution should be 1600 x 1200 pixels minimum. For a Wallet-size print, the image resolution should be 320 x 240 pixels minimum. Quality vs file size This guide shows you the kind of quality you can expect when you're printing out your photos.

Digital camera resolution vs print quality
Capture Resolution	Video Display	Print Size
		2x3"	4x5"/4x6"	5x7"	8x10"	11x14"	16x20"	20x30"
320x240	OK	Good	OK	Crap	Crap	Crap	Crap	Crap
640x480 0.3Megapixel	Good	Excellent	Good	Crap	Crap	Crap	Crap	Crap
800x600	Excellent	Photo Quality	Very Good	Reasonable	Crap	Crap	Crap	Crap
1024x768	Excellent	Photo Quality	Excellent	Good	OK	Crap	Crap	Crap
1280x960 1 MP	Excellent	Photo Quality	Photo Quality	Very Good	Good	Crap	Crap	Crap
1536x1180	Excellent	Photo Quality	Photo Quality	Excellent	Very Good	OK	Crap	Crap
1600x1200 2MP	Excellent	Photo Quality	Photo Quality	Photo Quality	Very Good	OK	OK	Crap
2048x1536 3 Megapixel	Excellent	Photo Quality	Photo Quality	Photo Quality	Excellent	Good	OK	OK
2240x1680 4 Megapixel	Excellent	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Very Good	Good	OK
2560x1920 5 Megapixel	Excellent	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Excellent	Very Good	Very Good
3032x2008 6 Megapixel	Excellent	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Excellent	Very Good
3072x2304 7 Megapixel	Excellent	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Excellent	Excellent
3264x2448 8 Megapixel	Excellent	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Excellent
10 Megapixel +	Excellent	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality	Photo Quality

Crap	Horribly pixelated blocky mess, like something out of 1987
OK	Looks reasonable enough, but nowhere near photo quality
Good	Pretty good all round, with a fair bit of detail
Very Good	This will be fine for most uses, unless you get up reeeeal close
Excellent	As good as a photo for most purposes
Photo Quality	Woohoo! Fantastic quality print, full of detail and perfect for your picture frame or for your showing off your very best shots.