# Fluid Sim Domain Size question

Hi there,

I know that in the past, you had to make the domain a square because blender only looked at the longest side to calculate the dimensions of the domain.

But recently i did a sim, made the domain a normal rectangle shape, to be nice and tidy and ram usage went down by a lot and sim speed increased as well very nicely

My question is. Did the devs change this in the fluid sim? Can we now use normal domains, tidy and made as tight as possible to avoid over use of memory? All the big fluid sim apps have this, and it seems blender has it now as well, but i saw no change in the wiki, they still say to create a cube as a domain.

What are your ideas on this subject?

This is the way that it’s always been.
The Square is the 2D equivalent of a 3D Cube.
The Rectangle is the 2D equivalent of a 3D Cuboid.

The domain is divided into little cubes called Fluid Voxels. I like to think of it as a box of those little sugar cubes.
The size of each Fluid Voxel cube is determined by the longest side of your domain, divided by the Final Resolutions setting that you set.
By keeping the Domain as “tight” to the fluid components as possible, you reduce the number of Fluid Voxels that are involved, thus reducing the amount of calculations needed and, also reduce the baking time.
The only thing is that you also need to keep your Domain large enough so that you don’t get fluid splashing against the side of your domain, creating that fluid hitting an invisible wall effect.

I know all of that, i work with 3dsmax and fumefx everyday so i’m well aquainted with voxel grids :).

Well, why would the wiki tell you to keep the domain a cube. A cube has equal sides, you cannot really make it tight on the sim. And i used to sim with 2.43 and if i remember correctly, i didn’t care that i changed the dimensions of the cube to fit the area. The fluid just ignored them and followed a virtual cube using the biggest side of my domain.

Now, in 2.62 i find out that this is not the case anymore, which is really good.

I can’t say that I’ve seen any difference in how the domain size works in the current blender and previous 2.4 versions.