Are there any rules for how big a jpg needs to be in order to print at high quality?

Web images are generally thought of in PPI (pixels per inch). So let’s say we have a JPEG image at 640X480 and you want to print it at 300dpi (DPI is dots per inch and is the print standard. 300dpi is minimum required for a quality printed image.).Divide your pixels by the resolution dots. Take 640 and divide by 300 and 480 divided by 300. You get 2.13 x1.6 so if you print this picture you will get a 2.13″ x1.6″ at 300dpi.

Let’s try the same priciple backwards. Say you want to print an 8X10 picture at 300 dpi. How big should your JPEG be?Multiply the DPI x THE SIZE OF THE PRINT. 300 times 8 is 2400 and 300 times 10 is 3000. You would need a JPEG at 2400 X 3000.

Take a look at this basic conversion: Based on 72ppi images to 300dpi.

IMAGE SIZE: 640 x 480 at 72ppi

PRINT SIZE: 2.13″ x 1.2″

IMAGE SIZE: 1200 x 1800 at 72ppi

PRINT SIZE: 4″ x 6″

IMAGE SIZE: 1500 x 2100 at 72ppi

PRINT SIZE: 5″ x 7″

IMAGE SIZE: 2400 x 3000 at 72ppi

PRINT SIZE: 8″ x 10″