Real word scale from image that does not state the size

[Jadefox]

Hi Guys

Tried searching the answer , could not quite find it.
Can anybody assist me with the following please ?
I am trying to make myself a standard material library and textures like
Arroway where they specifically state the size in m ( eg 3m x 3m ) I can set the real world scale and the mapping is done
But when I download a texture that does not specifically state its size in m or cm but only resolution , is there any way to
know how big to set its size to ?

[burnin]

Scientifically correct: No.
Artistically fine: Yes...

• by experience, skilled artist's eye.
• by clients wish/demand.

Notes:
- From architectural standpoint, 5% offset is an acceptable tolerance.
- Good web source of reference: http://www.wood-database.com/
- Nice printed source of reference (with 1:1 images of sanded VS sealed wood): The Real Wood Bible: The Complete Illustrated Guide to Choosing and Using 100 Decorative Woods   
- Every tree has its own life thus pattern ;)

[mferster]

look at other photo references and estimate the size. If you are dealing with common construction materials such as CMU, bricks, and hardwood planks they often come in standard sizes so you should be able to deduce the size of a map by the size of a individual bricks.

I'm always in the habit of observing and making mental notes of things like relative dimensions of objects & material finishes when I'm out and about in order to inform and improve my rendering practice.

[Jadefox]

Thanks guys, it makes a lot of sense.
Appreciate the help