How this instrument works
Both units are SI decimal fractions of the metre: nano- means 10⁻⁹ and micro- means 10⁻⁶, prefixes formalised together when the International System of Units was ratified in 1960. Before that standardisation, scientific papers from the 1940s and 1950s commonly wrote nanometre-scale lengths as 'millimicrons', abbreviated mµ — a thousandth of a micron — a term that has almost entirely disappeared from modern use in favour of the cleaner nanometre.
The ratio between them, 0.001, is a fixed power of ten rather than a measured quantity, so this conversion carries no uncertainty whatsoever; the same relationship holds no matter how the metre itself has been redefined, most recently in 1983 against the speed of light in a vacuum. Multiplying by 0.001 simply moves a decimal point three places left, and reversing it moves that same point three places right.
Each unit rules a different scale of the visible and near-invisible world. Micrometres describe the everyday microscopic — most bacteria measure 1 to 10 µm across, and a human hair runs roughly 70 to 100 µm thick. Nanometres describe what sits below that: viruses typically span 20 to 300 nm, visible light runs from about 380 to 700 nm, and modern computer chips are fabricated using features measured in tens of nanometres. Converting between the two is routine wherever biology, optics and materials science overlap.
- Type your value into the Nanometres (nm) field; it opens at 500, near the middle of the visible spectrum.
- Read your result on the Micrometres (um) line, recalculated to six decimal places on every keystroke.
- Going the other way? Multiply your micrometre figure by 1000 to return to nanometres exactly.
- For very small or very large entries, the field accepts thousandths, so values like 12.5 or 0.75 nm work without trouble.
Worked example — a 500 nm laser diode
Optics catalogues sometimes specify a laser diode's output wavelength in nanometres, and 500 nm sits near the blue-green edge of the visible spectrum, close to where human colour vision begins registering green light. Type 500 into Nanometres (nm) and Micrometres (um) reads 0.5 exactly — half of one micrometre, since 500 × 0.001 leaves nothing to round.
That same figure helps compare scales that otherwise feel abstract: a typical bacterium spans roughly 1 to 5 µm, so this 0.5 µm wavelength is smaller than most single bacterial cells, yet it is still one thousand times larger than a single nanometre — the rough diameter of a strand of DNA. Nanometres and micrometres describe neighbouring rungs on the same ladder, three orders of magnitude apart.
Questions
Is the nanometre-to-micrometre factor of 0.001 exact?
Yes, completely. Both nano- and micro- are SI prefixes defined as fixed powers of ten — 10⁻⁹ and 10⁻⁶ respectively — so their ratio is exactly 1000, or 0.001 in the other direction, with no measurement uncertainty at all. This holds regardless of how the underlying metre has been defined historically, because both units are tied to that same metre and shift together whenever it is redefined.
What did scientists call a nanometre before 1960?
Most commonly a 'millimicron', written mµ, meaning one thousandth of a micron — the older name for what SI now calls a micrometre. Mid-20th-century optics and biology papers used millimicrons routinely for wavelengths and cell structures. The term faded quickly once nano- was formally adopted as an SI prefix in 1960, and it is now rare enough that it mostly turns up when reading older scientific literature.
How big is a virus compared to a bacterium in these units?
Roughly ten to a hundred times smaller. Most bacteria measure between 1 and 10 micrometres across, easily visible under an ordinary light microscope, while viruses typically span only 20 to 300 nanometres — well below what visible-light microscopy can resolve, which is why electron microscopes are needed to see them directly. This is also why laboratory filters rated to stop bacteria, at roughly 0.2 µm, do not reliably stop viruses.
Why did semiconductor process names shift from microns to nanometres?
Because the transistor features chipmakers were fabricating kept shrinking below one micrometre through the 1990s, and naming a manufacturing process by its smallest feature size naturally moved into nanometre figures as those features passed below 1000 nm. Early processes were marketed in fractions of a micron before the industry settled on plain nanometre figures for newer generations — though modern node names are now largely marketing labels rather than a literal measurement of any single feature.
What part of the spectrum does 500 nm fall in?
The blue-green region, close to where the human eye's green-sensitive cone cells reach peak sensitivity. Visible light spans roughly 380 nm at the violet end to about 700 nm at the red end, so 500 nm sits a little past the midpoint, associated with cyan and blue-green hues rather than the pure green typically placed nearer 530 to 560 nm.
Can I convert directly from nanometres to millimetres instead?
Yes — multiply nanometres by 0.000001, or equivalently divide by 1,000,000, since a millimetre holds a million nanometres. Micrometres sit conveniently between the two: multiplying nanometres by 0.001 gets micrometres, and multiplying that result by 0.001 again gets millimetres, which is often easier to track mentally than jumping six orders of magnitude in a single step.