how much water blender put in the default cube??
I’m not quite sure what you are asking for over here? Maybe try to rephrase it!
i want to know whats the mesures of blender
for exemple, the default cube in the center, which its length is 2,
but how big is it in real word, 2cm? 2mm?
Ok so I get the question now - the realistic physical dimenions set by default by Blender. Sorry I dont have the answer to this, however I have a similar query.
In Addition to “In Taipei’s” query, is there a script of function that could display or get the real physical dimensions of any scaled object? Hopefully a Blender pro would pick up on this thread 
It doesn’t really matter…because you can scale things up to as big, or as small as you want. Just make sure all the proportions are right if you want to create a convincing scene.
I guess it doesnt matter - however, say I want to export a model from Blender to say a game engine and need the physical dimensions and scaling for other objects to be included - if you get an idea of what I mean.
There must be a way! What if I wanted to create a 100mt X 100mt small terrain - how do I know how much do I have to scale?
Everything is relative…if something sticks out you can always scale it to the right size. Heck, you can even adjust the size of the Blender grid itself if needed. Just make sure everything looks right for the camera! 
For exporting, I guess, it depends on how the game engine, and export script, handles blender units.
um…but it does matter when it comes to water simulation,
how do you know how much water you hav created?
actually i want to rebuild this scen,cause it looks beautiful…
http://www.blender.org/cms/typo3temp/pics/f6f23780c0.jpg
i think the size of the domain in picture is about 100cm
but i hav no idea how large should i scale the domain box in blender
OHHHHhhhhh… :o Silly me.
Select your domain and go to the physics/simulation tab. There’s a button called ‘advanced’ somewhere in the fluidsim settings. Select it, and you’ll see a field where you can input the real-world dimension of a Blender unit. Or that’s what I remember.
Have a nice day!
Ah-ha there we go. But what - thats only for fluids right! Lemme see if there is a similar button for general objects!
It simply doesn’t matter! There is no such concept as a metre to a computer. If you want it bigger, scale everything.
But what when you create a scale model, isn’t it relative to a real model. I understand that the models can be created by a scale (example 1cm = 1 default blender unit) - but how do we know what scale it is in real dimensions.
Are you sure there is no concept of a meter on a computer. Is it really all relative?
Absolutely! It can be anything you want it to be…
But what if you send your Model to one of the Rapid Prototyping Companys?
Would be interesting how big one default Blender Unit will turn out to be then…
Select your domain and go to the physics/simulation tab. There’s a button called ‘advanced’ somewhere in the fluidsim settings. Select it, and you’ll see a field where you can input the real-world dimension of a Blender unit. Or that’s what I remember.
thanks yu_wang! i got it
Someday - I will understand Blender!
Me too