Look up the dpi for your device here, e.g. iPhone 5 326 dpi, Macbook Pro Retina 221 dpi.
Support us! This is just a fun little idea, hastily implemented. Actually we build apps. Buy them. Send us a photo of your ruler. Follow us on Twitter.
Thanks Big respect goes to James Hall for jsPDF and Lea Verou for the initial inspiration by creating dpi.lv. Fork us on Github.
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