That's About the Size of It (2025 Edition)

Inspired by Isaac Asimov’s original essay, first published in
[The Magazine of Fantasy and Science Fiction (October 1961)](https://archive.org/details/Fantasy_Science_Fiction_v021n04_1961-10_PDF/page/n67/mode/2up),
and later collected in **Asimov on Numbers** (1977, Part Five: *Numbers and Biology*, Essay 13).

---

## The Origins of an Idea

When Isaac Asimov first wrote *“That’s About the Size of It”* for *The Magazine of Fantasy and Science Fiction* in 1961, he did what few science popularizers could. He took something vast and confusing and made it easy to understand.

By arranging animals on a **logarithmic scale of weight**, he showed how creatures of wildly different sizes could be compared fairly. From the might of the blue whale to the tiny rotifer, everything fit neatly within sixteen powers of ten.

When he later reprinted the essay in *Asimov on Numbers* (1977), he left it untouched. It remains a perfect snapshot of mid-20th-century science. Whales, dinosaurs, beetles, and the calm confidence of someone who trusted numbers to explain the world.

Half a century later, science has changed many details, but not the method. The logarithm still puts giants and microbes on equal footing, and life's full range still fits between roughly **10⁸** grams and **10⁻⁸** grams.

## Giants Reconsidered

The **blue whale** still rules as the largest creature ever to live, reaching up to 180 metric tons ([NOAA](https://www.fisheries.noaa.gov/species/blue-whale)). On a logarithmic scale, that gives it a value of 8.08. But new discoveries have changed the order of giants on land.

The *Brachiosaurus* of Asimov's table has been surpassed by **[Argentinosaurus huinculensis](https://www.nhm.ac.uk/discover/news/2017/may/new-study-reveals-titanosaur-was-one-of-biggest-animals-ever.html)** other titanosaur dinosaurs from South America. With estimated masses between 70 and 100 tons, they reach about **log 7.9**, nearly matching the whale. From here on, all logarithmic values refer to log₁₀ of the creature’s mass in grams.

Among predators, Asimov's **Allosaurus** has lost its crown to **[Spinosaurus aegyptiacus](https://www.nationalgeographic.com/science/article/spinosaurus-most-dangerous-dinosaur)** a long, semi-aquatic hunter that likely weighed around 8 tons, or **log 6.9**.

Even the sea has offered surprises. The familiar giant squid has been overtaken by the colossal squid **[colossal squid (*Mesonychoteuthis hamiltoni*)](https://collections.tepapa.govt.nz/topic/1375)**, discovered in Antarctic waters, the heaviest invertebrate ever found, reaching aboutr 500 kilograms or **log 6.7**.

The largest land mammal, **Paraceratherium** (once called **Baluchitherium**), still holds its place. The bird record, however, has been refined. What was once described as **Vorombe titan** is now believed, through DNA evidence, to represent very large females of **Aepyornis maximus**. Either way, it remains the largest bird ever known, at about **log 5.8**.

## The Physics of Being Alive

As Asimov explained, biology must obey geometry. The **cube-square law** applies to every living thing. If an animal doubles in height, its weight increases eight times, but the strength of its bones only increases four times.

This is why ants can lift many times their own weight and elephants cannot jump. Physics sets the limits long before evolution fills in the details.

Metabolism follows similar rules. Small creatures burn energy quickly just to stay alive. Large creatures move slowly and carefully. These trade-offs define what sizes are possible. Nothing larger than a blue whale can exist without collapsing under its own weight, and nothing much smaller than a rotifer can survive as a complex organism.

On a logarithmic scale, all of life fits into a surprisingly short line. For such diversity, that compactness is remarkable.

## From Biology to Software
By now you're probably wondering why I am writing about pre-historic animals in blog focused on technology.

Today, software developers face a similar problem when working with data. Numbers often come in very different sizes. One value might be in the millions while another is close to zero. When this happens, patterns are hard to see, and systems can behave poorly.

In machine learning, developers solve this by **normalizing data**.

Normalization means changing numbers so they share a common scale while keeping their meaning. This is the same reason logarithms work so well. Instead of letting large values drown out small ones, we reshape the data so everything can be compared fairly.

One common method is called **standardization**. Each value is adjusted so the average becomes zero and the spread becomes one. The data is not made smaller or larger in truth. It is simply made easier to work with.

This matters for the same reason Asimov's table mattered. Without scaling, insight is lost.

## A Simple Code Example
Below is a short example using PyTorch, a popular machine learning library, that can be used to regenerated Asimov's table (Disclaimer: The code reconstructs weights from their logarithmic values to mirror Asimov's original values the goal is comparison with the new animal weights I added).

```python
import torch

# Animals and their log10(weight in grams) from the blog table
animals = [
"Blue whale", "Sperm whale", "Argentinosaurus", "Whale shark",
"Spinosaurus", "Paraceratherium", "Great white shark",
"African elephant", "Colossal squid", "Ocean sunfish",
"Saltwater crocodile", "Leatherback turtle", "Polar bear",
"Aepyornis maximus", "Galápagos tortoise", "Green anaconda",
"Ostrich", "Komodo dragon", "Homo sapiens",
"Chinese giant salamander", "Wandering albatross",
"Japanese spider crab", "Goliath beetle", "Bee hummingbird",
"Etruscan shrew", "Paedocypris progenetica",
"Paedophryne amauensis", "Fairy fly", "Rotifer"
]

log_weights = torch.tensor([
8.08, 7.83, 7.90, 7.61, 6.90, 7.26, 7.03, 6.99,
6.70, 6.20, 6.15, 5.93, 5.87, 5.82, 5.42, 5.32,
5.20, 5.05, 4.96, 4.60, 4.26, 4.20, 1.70, 0.18,
-2.70, -3.20, -3.30, -5.30, -8.22
], dtype=torch.float32)

# Reconstruct weights in grams from log values
weights = torch.pow(10, log_weights)

# Add a second feature (rough speed estimates) so normalization makes sense
speeds = torch.tensor([
50, 40, 30, 5, 25, 40, 56, 25, 10, 3,
24, 35, 40, 0, 1, 8, 70, 20, 28, 5,
85, 3, 5, 50, 10, 2, 1, 1, 0.1
], dtype=torch.float32)

data = torch.stack([weights, speeds], dim=1)

# One-line log transform (matches the blog table)
log_data = torch.log10(data[:, 0])

# Standardization
mean = data.mean(dim=0)
std = data.std(dim=0)
normalized = (data - mean) / std

# Render full table
print(f"{'Animal':25s} | {'Weight(g)':>12s} | {'log10(w)':>8s} | {'Norm(w)':>8s}")
print("-" * 70)

for i in range(len(animals)):
print(
f"{animals[i]:25s} | "
f"{data[i,0]:12.2e} | "
f"{log_data[i]:8.2f} | "
f"{normalized[i,0]:8.2f}"
)
```
You can play with the example yourself in **Google Colab**, a free, browser-based notebook where you can run the code without installing anything: [Try it in Colab](https://colab.research.google.com/drive/1LzrLlbCGOnzxoRFaD99YJuAXK3r-lsQ8?usp=sharing)

If you are interested in learning more about similar topics, the book [Machine Learning with PyTorch and Scikit-Learn: Develop machine learning and deep learning models with Python](https://amzn.to/4qc0y5s) by Sebastian Raschka, Yuxi Liu and Vahid Mirjalili is very relevant. It walks through real machine learning workflows in Python, including how to prepare and scale data, how to build models with scikit learn and PyTorch, and how to think about data transformations like the one I show in the code example. It is practical and code focused, which makes it a good next step for readers who want to go deeper than the simple normalization snippet here.

## **Table 1: The Scale of Life, 2025 Edition**

| Animal | Characteristic | Log₁₀ (Weight in grams) |
| --- | --- | --- |
| [Blue whale](https://www.fisheries.noaa.gov/species/blue-whale) | Largest of all animals | 8.08 |
| [Sperm whale](https://www.fisheries.noaa.gov/species/sperm-whale) | Largest carnivorous animal | 7.83 |
| [Argentinosaurus](https://en.wikipedia.org/wiki/Argentinosaurus) | Largest land animal (extinct) | 7.90 |
| [Whale shark](https://www.worldwildlife.org/species/whale-shark) | Largest fish | 7.61 |
| [Spinosaurus](https://www.nationalgeographic.com/science/article/spinosaurus-most-dangerous-dinosaur) | Largest land carnivore (extinct) | 6.90 |
| [Paraceratherium](https://en.wikipedia.org/wiki/Paraceratherium) | Largest land mammal (extinct) | 7.26 |
| [Great white shark](https://www.fisheries.noaa.gov/species/great-white-shark) | Largest carnivorous fish | 7.03 |
| [African elephant](https://www.worldwildlife.org/species/african-elephant) | Largest land animal (alive) | 6.99 |
| [Colossal squid](https://collections.tepapa.govt.nz/topic/1375) | Largest invertebrate | 6.70 |
| [Ocean sunfish (*Mola mola*)](https://oceana.org/marine-life/ocean-sunfish/) | Largest bony fish | 6.20 |
| [Saltwater crocodile](https://australian.museum/learn/animals/reptiles/saltwater-crocodile/) | Largest reptile (alive) | 6.15 |
| [Leatherback turtle](https://oceanservice.noaa.gov/facts/leatherback.html) | Largest turtle | 5.93 |
| [Polar bear](https://www.worldwildlife.org/species/polar-bear) | Largest land carnivore (alive) | 5.87 |
| [Vorombe titan](https://royalsocietypublishing.org/doi/10.1098/rsos.180448)* | Largest bird (extinct) | 5.82 |
| [Galápagos tortoise](https://www.galapagos.org/about_galapagos/about-galapagos/galapagos-tortoise/) | Largest land reptile (alive) | 5.42 |
| [Green anaconda](https://www.nationalgeographic.com/animals/reptiles/facts/green-anaconda) | Heaviest snake | 5.32 |
| [Ostrich](https://animaldiversity.org/accounts/Struthio_camelus/) | Largest bird (alive) | 5.20 |
| [Komodo dragon](https://www.nationalgeographic.com/animals/reptiles/facts/komodo-dragon) | Largest lizard | 5.05 |
| [*Homo sapiens*](https://www.britannica.com/topic/Homo-sapiens) | Largest primate | 4.96 |
| [Chinese giant salamander](https://amphibiaweb.org/species/5185) | Largest amphibian | 4.60 |
| [Wandering albatross](https://www.britannica.com/animal/wandering-albatross) | Largest flying bird | 4.26 |
| [Japanese spider crab](https://www.montereybayaquarium.org/animals/animals-a-to-z/japanese-spider-crab) | Largest arthropod | 4.20 |
| [Goliath beetle](https://en.wikipedia.org/wiki/Goliathus) | Largest insect | 1.70 |
| [Bee hummingbird](https://www.birdlife.org/species/factsheet/bee-hummingbird-mellisuga-helenae) | Smallest bird | 0.18 |
| [Etruscan shrew](https://animaldiversity.org/accounts/Suncus_etruscus/) | Smallest mammal (by mass) | −2.70 |
| [*Paedocypris progenetica*](https://www.nature.com/articles/news060109-14) | Smallest fish (and vertebrate) | −3.20 |
| [*Paedophryne amauensis*](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0041510) | Smallest vertebrate (overall) | −3.30 |
| [Fairy fly](https://en.wikipedia.org/wiki/Fairyfly) | Smallest insect | −5.30 |
| [Rotifer](https://www.britannica.com/animal/rotifer) | Smallest multicelled creature | −8.22 |

* As mentioned previously, Vorombe titan has been reclassified through DNA analysis and is now considered to represent large females of Aepyornis maximus rather than a separate species.

## The Measure of Ourselves

If every living creature were placed on a single logarithmic line, it would fit on one page. Humans would sit near the middle. Not the largest. Not the smallest. But unique in one important way.

We are the ones who draw the line.

Asimov’s real gift was not the table itself, but the idea that numbers can make scale feel human. When used well, numbers invite curiosity instead of fear.

> When numbers are used not to intimidate but to illuminate,” he wrote, “they give us the measure of the world and of ourselves.

More than sixty years later, the names and measurements have changed, but the lesson has not. From the whale to the rotifer, that is about the size of it, **that is about the size of it.**

## References & Further Reading

1. [Asimov, I. (1961). “That’s About the Size of It.” *The Magazine of Fantasy and Science Fiction*, Oct. 1961.](https://archive.org/details/Fantasy_Science_Fiction_v021n04_1961-10_PDF/page/n67/mode/2up)

2. Asimov, I. (1977). *Asimov on Numbers*. Doubleday, Part Five: *Numbers and Biology*, Essay 13.

3. [Naish & Barrett (2018). *Dinosaurs: How They Lived and Evolved.* Smithsonian Books.](https://www.smithsonianbooks.com/store/science/dinosaurs-how-they-lived-and-evolved/)

4. [Royal Society Open Science (2018): “*Vorombe titan*, the world’s largest bird.”](https://royalsocietypublishing.org/doi/10.1098/rsos.180448)

5. [Rittmeyer et al. (2012). “Discovery of *Paedophryne amauensis*, the world’s smallest vertebrate.” *PLoS ONE*.](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0041510)

6. [Natural History Museum (London) dino directory profile](https://www.nhm.ac.uk/discover/dino-directory/spinosaurus.html)

7. [Museum of New Zealand Te Papa: “The Colossal Squid.”](https://www.tepapa.govt.nz/visit/exhibitions/colossal-squid)