Scale Explorer

Microscopic

How big is a hydrogen atom?

Hydrogen atom · Sized by the Bohr radius

Bohr radius
0.0000000000529177210544 m 52.9177 pm
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Hydrogen atom, Red blood cell, Human hair (width), Human drawn to the same scaleHydrogen atom: bohr radius 0.0000000000529177210544 m (too small to see at this scale). Red blood cell: diameter 7.5–8.7 µm (too small to see at this scale). Human hair (width): average diameter ≈ 70 µm (too small to see at this scale). Human: height 1.61–1.75 m.Hydrogen atom: 0.0000000000529177210544 m (too small to see at this scale)Red blood cell: 7.5–8.7 µm (too small to see at this scale)Human hair (width): ≈ 70 µm (too small to see at this scale)Human: 1.61–1.75 mHuman1.61–1.75 mHydrogen atom0.0000000000529177210544 m · too small to seeRed blood cell7.5–8.7 µm · too small to seeHuman hair (width)≈ 70 µm · too small to see

Hydrogen atom, Red blood cell and Human hair (width) are too small to see at this scale and are marked with ▲.

Everything is drawn to the same scale, standing on the same ground line. Silhouettes are simplified outlines scaled to the measured dimension. A faded outline shows the top of a size range.

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Dimensions

MeasurementMetricImperialNotesSource
Bohr radius 0.0000000000529177210544 m 52.9177 pm CODATA 2022 recommended value of the Bohr radius a0, 5.291 772 105 44(82) x 10^-11 m; standard uncertainty 0.000 000 000 82 x 10^-11 m (relative 1.6 x 10^-10). Used as the atom's radius, so the drawing is twice this wide. [1]

About the hydrogen atom

Hydrogen is the simplest atom, made of a single proton and a single electron. An atom has no hard edge, so its size is usually expressed through the Bohr radius, a fundamental physical constant that sets the natural length scale of the hydrogen atom. The CODATA 2022 value published by NIST is about 5.29 x 10^-11 m, a little over half of a ten-billionth of a metre.

  • NIST lists the Bohr radius with a relative standard uncertainty of 1.6 x 10^-10, making it one of the most precisely known lengths in physics. [1]

How many fit?

  • ≈ 32 billion × Hydrogen atom · bohr radius lined up end to end match the Human · height
  • ≈ 150,000 × Hydrogen atom · bohr radius lined up end to end match the Red blood cell · diameter

Counts divide one sourced figure by another. "End to end" uses each object's main measurement; weight and volume rows appear only when both figures are sourced.

How it compares

  • 1/150,000 A red blood cell is about 150,000 times as across as a hydrogen atom is in radius. See side by side
  • 1/1.3 million The width of a human hair is about 1.3 million times as wide as a hydrogen atom is in radius. See side by side
  • 1/1.2 million–38 million A grain of sand is about 1.2 million–38 million times as wide as a hydrogen atom is in radius. See side by side
  • 1/64 million–94 million A black garden ant is about 64 million–94 million times as long as a hydrogen atom is in radius. See side by side
  • 1/130 million A grain of rice is about 130 million times as long as a hydrogen atom is in radius. See side by side
  • 1/32 billion An average adult is about 32 billion times as tall as a hydrogen atom is in radius. See side by side

Factors compare the bohr radius of a hydrogen atom with each object’s own main measurement (height for a human). Where a size varies, the factor is given as a range.

Notes on these figures

  • An atom has no sharp boundary; the Bohr radius is a defined length scale (the electron's orbit radius in the Bohr model of hydrogen), not a measured edge, so drawing the atom as a disc of this radius is a convention.
  • No sourced mass for a hydrogen atom in kilograms was fetched, so mass is left out.

Sources

  1. NIST (CODATA 2022), CODATA Value: Bohr radius. Accessed 25 September 2026.

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