1
m
0.001
km
100
cm
1,000
mm
999,999,999.9999999
nm
10,000,000,000
Å
999,999,999,999,999.9
fm
39.37007874
in
3.2808399
ft
0.00062137
mi
6.6845871223e-12
AU
1.057000834025e-16
ly
3.240779289444e-17
pc
3.240779289444e-20
kpc
3.240779289444e-23
Mpc
6.18714250e+34
lP
1
m
0.001
km
100
cm
1,000
mm
999,999,999.9999999
nm
10,000,000,000
Å
999,999,999,999,999.9
fm
39.37007874
in
3.2808399
ft
0.00062137
mi
6.6845871223e-12
AU
1.057000834025e-16
ly
3.240779289444e-17
pc
3.240779289444e-20
kpc
3.240779289444e-23
Mpc
6.18714250e+34
lP
Length is the most fundamental geometric quantity, spanning an extraordinary range in physics — from the Planck length (1.616 × 10⁻³⁵ m, the smallest physically meaningful scale) to the observable universe radius (~4.4 × 10²⁶ m), a range of 61 orders of magnitude. This converter covers atomic, everyday, and astronomical length scales used across all branches of physics.
The metre (m) is the SI base unit of length, defined since 1983 as the distance light travels in vacuum in 1/299,792,458 seconds. This definition ties the metre to the exact speed of light and the second, making it reproducible anywhere in the universe. Key sub-units: 1 cm = 10⁻² m, 1 mm = 10⁻³ m, 1 micron (μm) = 10⁻⁶ m, 1 nanometre (nm) = 10⁻⁹ m, 1 picometre (pm) = 10⁻¹² m.
In atomic and molecular physics, the Angstrom (Å = 10⁻¹⁰ m = 0.1 nm) is the natural length scale — atomic radii are 0.5–2.5 Å, covalent bond lengths 1–3 Å, and DNA base-pair spacing 3.4 Å. The femtometre (fm = 10⁻¹⁵ m, also called a fermi) is the scale of atomic nuclei — proton radius ~0.84 fm, uranium nucleus ~7.4 fm.
In astronomy, distances are measured in astronomical units (AU = 1.496 × 10¹¹ m, Earth-Sun distance), light-years (ly = 9.461 × 10¹⁵ m), and parsecs (pc = 3.086 × 10¹⁶ m). One parsec is defined as the distance at which 1 AU subtends an angle of 1 arcsecond. The nearest star, Proxima Centauri, is 1.295 pc = 4.22 ly away. The observable universe is ~14.26 Gpc in radius.
Select the input unit and enter the value. All conversions pass through metres. Key exact conversions: 1 AU = 149,597,870,700 m (exact by IAU 2012), 1 ft = 0.3048 m (exact), 1 mile = 1609.344 m (exact), 1 ly = 9,460,730,472,580,800 m (exact), 1 pc = 3.085677581491367 × 10¹⁶ m.
Scale reference: atom diameter ~1 Å; DNA strand width ~2 nm; virus ~100 nm; bacterium ~1 μm; human hair ~75 μm; Earth diameter ~12,742 km; Earth-Sun ~1 AU = 150 million km; nearest star ~1.3 pc; Milky Way ~30 kpc diameter; Andromeda galaxy ~770 kpc away.
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1 parsec = 3.086 × 10^16 m = 206,265 AU = 3.2616 light-years. The parsec is the natural unit for stellar distances — Proxima Centauri is at 1.295 pc.
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The Bohr radius a₀ = 0.529 Å = 52.9 pm. This is the most probable distance of an electron from the proton in ground-state hydrogen, and the fundamental length scale of atomic physics.
The Planck length lP = √(ℏG/c³) = 1.616255 × 10⁻³⁵ m is the length scale at which quantum gravitational effects become important. Below this scale, our current theories of physics (quantum mechanics and general relativity) break down. It is about 10²⁰ times smaller than a proton. No experiment can probe this scale directly.
1 Å = 10⁻¹⁰ m = 0.1 nm. It was named after Swedish physicist Anders Jonas Angstrom (1814-1874), a pioneer of spectroscopy. It is not an SI unit but is widely used in crystallography, molecular biology, and surface science because atomic dimensions are conveniently expressed as whole numbers of Angstroms (e.g., C-C bond = 1.54 Å, water O-H = 0.96 Å).
1 AU = 149,597,870,700 m (exactly, by IAU 2012 definition). It is approximately the mean Earth-Sun distance. Key distances: Mercury 0.387 AU, Venus 0.723 AU, Earth 1.000 AU, Mars 1.524 AU, Jupiter 5.203 AU, Saturn 9.537 AU, Neptune 30.07 AU. The Voyager 1 spacecraft is currently about 165 AU from the Sun.
Both are astronomical distance units. 1 light-year = distance light travels in 1 year = 9.461 × 10¹⁵ m. 1 parsec = 3.086 × 10¹⁶ m = 3.2616 light-years. The parsec is based on stellar parallax geometry: 1 pc is the distance at which 1 AU subtends 1 arcsecond. Parsecs are preferred in professional astronomy; light-years in popular science.
1 fm = 10⁻¹⁵ m, named after Enrico Fermi. It is the characteristic scale of atomic nuclei. Proton radius ≈ 0.84 fm; neutron ≈ 0.9 fm; nuclear radius ≈ 1.2 × A^(1/3) fm (where A is mass number); heaviest nuclei ≈ 7-8 fm. The classical electron radius (2.82 fm) is also in this scale despite electrons having no measurable size down to 10⁻¹⁸ m.
The observable universe has a comoving radius of approximately 46.5 billion light-years = 14.26 Gpc = 4.4 × 10²⁶ m, despite the universe being only 13.8 billion years old. The larger size is due to the expansion of space: regions from which light has had 13.8 billion years to reach us have since moved much farther away due to cosmic expansion. The Hubble radius (where recession velocity = c) is about 14.4 Gly.
Since 1983, 1 metre is defined as the distance light travels in vacuum in 1/299,792,458 seconds. This makes the speed of light exactly 299,792,458 m/s by definition. The second is defined by the cesium-133 hyperfine transition (9,192,631,770 Hz exactly). Together, these definitions make the metre derivable from atomic physics with no reference to any physical object.
1 Mpc = 10⁶ pc = 3.086 × 10²² m = 3.26 million light-years. Megaparsecs are used for intergalactic and cosmological distances. The Andromeda Galaxy is 0.77 Mpc away. The Virgo Cluster center is ~16 Mpc. Hubble's constant is typically expressed in km/s/Mpc: H₀ ≈ 67-73 km/s/Mpc, meaning galaxies 1 Mpc away recede at 67-73 km/s.
Nanotechnology operates at 1-100 nm scales. Reference points: C-C bond 0.154 nm; DNA double helix diameter 2.0 nm; ribosome ~25 nm; typical protein 2-10 nm; cell membrane thickness ~7-10 nm; silicon transistor gate (2022) ~2-3 nm; virus 20-300 nm; bacterium 1-10 μm. At these scales, quantum effects, surface-to-volume ratios, and van der Waals forces dominate behavior.
The Hubble length c/H₀ ≈ 4280 Mpc ≈ 13.97 Gly defines the distance at which recession velocity equals the speed of light in the current epoch. This is the Hubble radius or Hubble horizon — not a hard boundary, but the scale of the currently observable universe's Hubble sphere. It grows as the universe expands and H decreases.
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