What "3 nm" really means

When a company announces a "3 nm" chip, it is natural to picture something measuring three nanometres. There is nothing in the chip that measures three nanometres. The number is a name.

It used to mean something

For a long time, the node name was tied to a real size. In the 1990s and early 2000s, the labels 250 nm, 180 nm, 130 nm and so on tracked a real dimension of the transistor, such as the length of its gate. Each new generation shrank those features by roughly 30 percent, and the name followed.

Then the shrinking changed shape

Around the 2010s, making transistors smaller stopped being a matter of scaling the same design down. Engineers changed the design itself. Transistors went three-dimensional, with a thin fin of silicon standing up so the gate could wrap around it. Later designs wrap the gate around the channel from every side.

Once the improvements came from new shapes and new materials as much as from smaller dimensions, a single size no longer described a generation. But companies kept the naming habit. The number kept going down with each generation, even though it no longer matched a measurement.

What the real sizes are

The smallest features on a chip marketed as "3 nm" are measured in tens of nanometres. Commonly cited figures put the spacing between transistor gates at roughly 45 to 50 nanometres and the spacing between the finest metal wires at roughly 20 to 25. Sources differ, and the companies publish different numbers, so treat these as rough.

The point is that the label is much smaller than anything you could find with a ruler.

The names are not comparable

Because the number is a marketing label, "3 nm" from one manufacturer is not the same as "3 nm" from another. In 2021 Intel renamed its nodes to line up better with what its competitors were doing, so a name like "Intel 7" does not mean 7 nanometres either.

So a bare node name tells you the rough era of a chip, and not much more.

What to compare instead

A few measures say more.

• Transistor density. How many millions of transistors fit in a square millimetre. This is closer to a real, comparable measure of how much a manufacturer can pack in.
• Performance and power. How fast the chip runs at a given power, and how much energy it needs for the same work. This is what you actually feel.
• The design itself. A well-designed chip on an older node can beat a poor design on a newer one.

The short version

"3 nm" is a label for a generation of chip making. It is not a size. Next time you see a node name in a headline, read it as "the newest generation", then look for density and performance numbers.

Making any of these chips is still remarkable. The lithography machines that print the finest layers use light with a wavelength of 13.5 nanometres, called extreme ultraviolet. How that works is a story for another Deep Dive.