I see all these epic builds that are super detailed and look real from a distance, but none of them say what the scale ratio is. What is the best scale to use for great detail like that? I've started a project using 4:1 but am not sure if that's enough or too much. Also, how does 3:1 or 2:1 even work? You can't fill a square with 3 blocks. Or 2....then it's a rectangle...
A scale of 2:1 just means that every dimension is 2x that of the original object (making the object actually 8x larger in volume). So if you're modeling a house that is 75' wide by 30' deep and you presume a block is approximately 3' square, then at 1:1 your house would be 25 blocks by 10 blocks and the smallest detail you could show is 3' in size. Half-slabs, stairs, fence posts, doors, etc. can help with smaller details even at 1:1.
If you scale up to 2:1, then the house becomes 50 blocks by 20 blocks and you could show detail as small as 1.5'.
At 3:1 the house is 75 blocks x 30 blocks and a detail 1' x 1' x 1' is modelable (within the limits of the blocks we have anyway).
I haven't built any detailed realistic builds myself, but I'd think my starting point would be to answer the question, "how big is the smallest detail I want to show?" and then work up from there to the correct scale. If the smallest detail you want to show is 1" and the object's largest dimension is 12', then you would need 144 blocks for that longest dimension (432 feet, if each block is 3 feet on a side) resulting in a scale of 432:12 or 36:1.
In general the larger the thing is you're trying to model, the smaller the scale needs to be. Modeling the Death Star requires .01:1, modeling an ant requires 1000:1 (I'm totally guessing).