What Size Do I Need?

By far the most frequent question we get is how big you will need a scan to be in order to to achieve a certain print size.  The easiest way to figure this out is to use the scan calculator at right (desktop) or below (mobile) but if you’re super DIY and want to figure it out yourself, use the following calculations:

 

First, you need to figure out what your print resolution is going to be.  The most standard is 300dpi, but some printers print up to 360.  Next, you will need to do some simple math in order to figure out what the final pixel dimensions of your image need to be.  If you want to make a 20×30 print, you will need on the long edge 300 (dots per inch) x 30 (inches) = 9,000 (dots, or pixels).  On the short edge, you will need 300 dpi x 20 inches = 6,000 pixels.  So, your final file will need to be 9000×6000 pixels.

Working backward, if you are working from a 35mm negative, your original is 24x36mm or 1×1.5 inches.  So just divide – 9,000 / 1.5 (long edge / long edge) = 6,000.  Short edge would be 6,000/1, which fortunately produces the same answer!  If we were going to crop, we might have to do the math for both the long and short edge and pick the higher resolution.  Therefore, you would need a minimum 6,000 ppi scan to make your 20×30 print from your 35mm negative.  In practice it’s best to leave a bit of headroom for crops and downsampling, so you should order a 7,000 or even 8,000 ppi scan just to be on the safe side.

 

All our scans are 16bit RGB (or 48 bits total), and the formula for file size is:

( horizontal pixels × vertical pixels × bit depth) / (8 [to convert to bytes] × 1024  [kilobytes] ).  So, for the above example:

6000*9000*48 = 2,592,000,000 / (8×1024) = 316406.25 kb or 316.40 mb

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