Save PowerPoint slides in a specific size

One of my current projects at work is to investigate a screen saver to display images whether or not there is a user logged on or not (there will be a blog on the entire process shortly).

As part of this I wanted to create some sample images and text to demonstrate the system. Whilst I’m no expert in graphic design, I like to use PowerPoint 2010 as it has some really nice effects and can produce some great Web 2.0 style graphics.

One of the areas that keeps causing me issues is that all the measurement are in cm or inches, rather than pixels. This means that I have to guess how large to make the graphic, usually resulting in some tweaking afterwards.

After a bit of investigation I found a couple of useful articles:

Improve PowerPoint’s GIF, BMP, PNG, JPG export resolution
Save PowerPoint Slides as Images

Essentially, the number of pixels is calculated by multiplying the slide width or height by the screen DPI (or Dots Per Inch). This seems to vary depending on which version of PowerPoint you are using (and even by service pack), however, it is usually 72, 96 or 120.

Brilliant! Problem solved…. Well, not quite. As I’m in the UK, Microsoft Office has defaulted to the metric measurement, so I have to perform an additional calculation to convert to centimetres.

So here’s the formula:

length = (Pixels/96) * 2.54

For example, if we wanted 1024 pixels, we would calculate the length by dividing 1024 by 96 (resulting in 10.666 inches), then multiply by 2.54 to give 27.093 cm. Here’s a table with some common size that you may find useful:

Pixels		Inches		Cm		Ratio
Width	Height	Width	Height	Width	Height	W/H
320	240	3.33	2.50	8.47	6.35	1.33
480	320	5.00	3.33	12.70	8.47	1.50
640	480	6.67	5.00	16.93	12.70	1.33
800	600	8.33	6.25	21.17	15.88	1.33
1024	768	10.67	8.00	27.09	20.32	1.33
1080	720	11.25	7.50	28.58	19.05	1.50
1280	720	13.33	7.50	33.87	19.05	1.78
1280	1024	13.33	10.67	33.87	27.09	1.25