How this instrument works
Anders Jonas Ångström, professor of physics at Uppsala, published his atlas of solar radiation in 1868 with every wavelength expressed in units of one ten-millionth of the millimetre. That step of 10⁻¹⁰ m fitted spectral data so comfortably that colleagues across Europe borrowed it, and by 1907 it carried his name. Atoms sit roughly one such unit wide, which is why this Swedish convenience outlived its inventor by 150 years.
Both units on this sheet are exact decimal powers of the metre, so no measurement enters anywhere. An angstrom is 10⁻¹⁰ m; nano- was ratified as an SI prefix meaning 10⁻⁹ by CGPM in 1960. Dividing one into another leaves 0.1 with no remainder and no uncertainty — arithmetic that merely walks the decimal point one place left. Before 1960 that was not quite true: an international ångström defined in 1907 against the red cadmium emission line ran about two parts in ten million longer than 10⁻¹⁰ m, and only redefining the metre against krypton-86 radiation swept that discrepancy away.
Preference splits neatly by trade. Crystallographers, structural biologists and quantum chemists count in angstroms — carbon–carbon single bonds span 1.54 Å, silicon's lattice constant is 5.431 Å, copper Kα X-rays arrive at 1.5406 Å, and any protein solved at 1.8 Å resolution counts as good. Optics, photolithography and thin-film work counts in nanometres instead: visible light spans 380–700 nm, argon-fluoride steppers print at 193 nm, extreme-ultraviolet scanners at 13.5 nm. Identical lengths, different dialects — moving between them is this converter's whole job.
- Type your measurement into Angstroms (A); 10 Å sits there as your starting point.
- Read Nanometres (nm) directly beneath, recomputed with every keystroke.
- Going from nanometres back to angstroms? Multiply your figure by 10 and enter that value in Angstroms (A).
- Results carry six decimals — sub-picometre detail, finer than any bond length or lattice spacing needs.
Worked example — ten angstroms of alumina
An atomic-layer deposition cycle lays down close to one angstrom of alumina, so after ten cycles the process engineer records film thickness as 10 Å. The customer's optical specification, written by people who think in nanometres, wants that figure their way. Enter 10 into Angstroms (A) and Nanometres (nm) returns 1.0 — one nanometre, exactly, with nothing rounded away.
Check it against something physical: DNA's double helix measures roughly 20 Å across, so this coating is half that width. Scaling behaves identically in both directions — 0.5 Å becomes 0.05 nm, 2500 Å becomes 250 nm — because multiplying by exactly 0.1 shifts the decimal point and does nothing else.
Questions
Is one angstrom exactly 0.1 nanometres?
Yes, exactly — by definition rather than by measurement. An angstrom is fixed at 10⁻¹⁰ metres and the nanometre at 10⁻⁹ metres, so their ratio is precisely one tenth and carries no uncertainty at all. Every digit you see in your result comes from your own entry, never from this factor. Multiply angstroms by 0.1 going one way; multiply nanometres by 10 coming back.
Is the angstrom an SI unit?
No. It is one of several non-SI units that BIPM and NIST both discourage, and NIST Special Publication 811 places it among units to avoid in new work, preferring nanometres or picometres. Its survival in crystallography and spectroscopy owes to generations of literature, diffraction software and structure databases already written in it — plus one happy accident of scale, since atomic diameters land near 1 Å.
Should I be using picometres instead?
Several chemistry journals and IUPAC recommendations do prefer them. One angstrom is exactly 100 pm, so that carbon–carbon bond becomes 154 pm — an integer with no decimal point to mislay — and the picometre, unlike the angstrom, is a proper SI submultiple. Conversion stays trivial: angstroms to picometres, multiply by 100; picometres to nanometres, divide by 1000.
What do people most often get wrong here?
Direction. Angstroms are smaller, so numeric values shrink tenfold on their way to nanometres: 25 Å is 2.5 nm, never 250 nm. Symbols cause trouble too — Å is not A for ampere, and nm is neither NM for nautical mile nor nmol for nanomole. Before trusting any figure lifted from data files or plot axes, confirm which unit their headers actually declare.
Has an angstrom always been this exact length?
Not quite. An international definition from 1907 pinned it to red cadmium's emission line rather than to the metre, making one international ångström about 1.0000002 × 10⁻¹⁰ m — some two parts in ten million adrift. Redefining the metre in 1960 against krypton-86 radiation closed that gap, and the angstrom has held at exactly 10⁻¹⁰ m ever since. Wavelength tables printed before then can still carry that faint offset.
Why do protein structures quote resolution in angstroms?
Because diffraction resolution corresponds to Bragg spacing, and useful spacings fall between roughly 1 and 4 Å — single-digit numbers crystallographers can compare at sight. Structures at 1.5 Å resolve individual atoms; those at 3.5 Å show little beyond backbone traces. Expressed in nanometres they become 0.15 and 0.35, which is why structure databases have kept angstroms.