By common convention biggish things are compared with a human’s height and smallish things with a human’s strand of hair, which at 10-3.6 is almost at the limit of what you can see with the naked eye, which coincidentally is almost exactly the size of a human egg. That is a point of reference, in the best anthropomorphic sense.
Now further help is at hand from Cary Huang http://htwins.net/scale2/
Down at 10-5.1 you can see white and red blood cells, the cell nucleus, the X chromosome and e.coli .
You have to go further down to 10-6.2 to see the largest virus and the smallest thing visible to a light microscope. This is the level of scale called a micrometer because it is a millionth of a meter (6 zeros).
Deeper still are the HIV virus and the transistor gate, both at 10-7.1. It is only at this point that we can start talking about computational scale. If the binary digit has a size, it is roughly 25 nanometers at the moment, but may get smaller.
Drill down further, and at 10-8.2 we get to biological code, DNA. This must be a key reference dimension. All of you is there, in compact informational form. This is stuff which can truly be called “causal”.
Or you could set it precisely at a nanometer which is a billionth of a meter (9 zeros) at which scale you can see a molecule of glucose, about which we hear so much in neurology. It is our basic unit of energy, the simplest sugar which keeps us going. For the more technological, carbon nanotubes are at this scale.
Previously, in “The Enchanted Loom” I was talking about the scale we need to use if we are to understand how the brain functions. I think that we are going to have to work at somewhere between 10-8.2 and 10-9 before we really get to the bottom of biological things. After that, all we have to do is work out how everything interacts, and can be scaled up into explaining how you read and understood this sentence.