Is there any way to estimate the exterior sq. footage of your house if you know the interior sq. footage?

Or would you just have to measure everything?
Are you planning on painting? If you know the height of your ceilings (e.g., 10 foot), then just count the number of floors you have. Multiply by ceiling height plus 1 foot, then multiply by the distance around your house. That will get close enough for rough estimate. If you are buying siding, then I would actually measure.