In the spirit of going back to school, we have posted some information on file sizes for your digital printing.
COMMON SIZES AND THEIR MB SIZE
When you double the resolution, (150 to 300), you increase the Mb size by 4 times. That is why the big difference between 150 and 300 dpi.
Ex: An 8×10 at 200% = 16×20, which has an area 4 times that of an 8×10.
Megabyte size of a file equals length in pixels X height in pixels X the number of channels (3 for RGB and 1 for Grayscale). To convert inches to pixels, multiply the inches dimensions by 25.4 (25.4mm to the inch) Resolution, (DPI), is based on the metric system. Res 40 actually means 40 pixels per mm, so multiply inches by 24.4 you can figure out pixel size. Do this for both dimensions and multiply both numbers together, then multiply that number by 1 or 3, depending on the color space. The answer is your megabyte size. Remember that one million bytes to the megabyte so count 6 places from the right to place the decimal point.
Ex: 4″x5″ at 300 dpi = ?Mb 4″x300 dpi = 1200 pixels, 5″x300 dpi = 1500 pixels, 1200×1500 = 1800000, 1800000 x 3 (rgb) = 5400000. Move he decimal 6 place from the right and you have the file size of 5.4 Mb.