I use this to check scale on my models and ones I download. One of my less exciting files to look at but hopefully it gets a blender user on the right path to proper scaling. Scaling isn't subjective, it should be correct whether it is "1 to 1" or not. Later on in the modelling process scale can will come back to haunt you. Materials, Exporting, Cameras, Compositing, Modifiers are all affected by it.
The scale starts from a 6' or 1.83m male silouhette then to a car, elephant, bus, F16, 747 and Star Trek Enterprise. If you tab into edit mode on one of the silouhettes, the dimensions are switched on. They aren't exact put within a few inches. As a Canadian, I live somewhere between the US and Europe as far as to which unit of measure I use. Somedays metric, somedays imperial, most days Blender units.