# How to calculate map distances from scale

I have this PDF image of a map with a scale of 1:300. How do I obtain the real length of the object precisely, since it can be zoomed in and out?

Let's just say that I want to calculate the length of this Storage room From what I have been researching, it seems I need to have the DPI of the image. After I have the DPI what do I have to do to get the length?

Will it give me the 1:300 scale if I print the image?

• The physical page size of the PDF is fixed. The size of this storage room can be expressed as a fraction of the total page (at any size), and the real page size will give you the 'real' scaled size. Then it's times 300 that. – usr2564301 Apr 9 '16 at 17:12
• – Dom Apr 11 '16 at 12:10

You may be over-thinking this. If the scale is 1:300, all you need to do is multiply the current dimension you want to calculate by 300.

For instance if the storage room is 20mm wide:

2cm × 300 = 600cm = 6m

Your storage room is 6m wide.

If you were only capable of measuring in pixels, you would need to know the PPI of the image to calculate the correct physical measurement, you can however measure physical distances in PDFs relatively easy, that depends on the software you are using though. 