How big is an E. coli bacterium?

E. coli bacterium · Escherichia coli

Length: ≈ 2 µm 2 µm approx.
Diameter (width): ≈ 1 µm 1 µm approx.
Volume: ≈ 0.000000000001 cm³ 0.000000000000034 US fl oz approx.
Mass: ≈ 0.000000000001 g 0.0000000000000022 lb approx.

E. coli bacterium, 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

Measurements of E. coli bacterium
Measurement	Metric	Imperial	Notes	Source
Length	≈ 2 µm	≈ 2 µm	Rule-of-thumb cell length based on light and electron microscopy. Approximate	[1]
Diameter (width)	≈ 1 µm	≈ 1 µm	Rule-of-thumb cell diameter. Approximate	[1]
Volume	≈ 0.000000000001 cm³	≈ 0.000000000000034 US fl oz	Stated as about 1 µm³ (1 fL); 1 µm³ = 1e-12 cm³. Volumes range from about 0.4 to 2.5 µm³ depending on growth rate. Approximate	[1]
Mass	≈ 0.000000000001 g	≈ 0.0000000000000022 lb	Stated as about 1 pg (1e-12 g), estimated from the 1 µm³ volume at the density of water. Approximate	[1]

About the E. coli bacterium

Escherichia coli is a rod-shaped bacterium that lives in the gut and is one of the most studied organisms in biology. Its shape is close to a cylinder with rounded ends. A widely used rule of thumb puts a cell at about 2 µm long and 1 µm wide, with a volume near 1 cubic micrometre and a mass of about a picogram, though cell size changes with growth conditions.

Faster-growing cells are larger: E. coli dry mass differs about five-fold between slow- and fast-growing cultures. [1]
Treating the cell as a cylinder with hemispherical caps, 1 µm wide and 2 µm long, gives a volume of about 1.3 µm³. [1]

How many fit?

≈ 840,000 × E. coli bacterium · length lined up end to end match the Human · height
≈ 8.4 × 10¹⁶ × E. coli bacterium · mass on the scales weigh as much as Human · body mass
≈ 4 × E. coli bacterium · length lined up end to end match the Red blood cell · diameter
≈ 94 × E. coli bacterium · volume packed inside, by volume fill Red blood cell · cytosol volume

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

1/4 A red blood cell is about 4 times as across as an E. coli bacterium is long. See side by side
1/35 The width of a human hair is about 35 times as wide as an E. coli bacterium is long. See side by side
1/31–1,000 A grain of sand is about 31–1,000 times as wide as an E. coli bacterium is long. See side by side
1/1,700–2,500 A black garden ant is about 1,700–2,500 times as long as an E. coli bacterium. See side by side
1/3,500 A grain of rice is about 3,500 times as long as an E. coli bacterium. See side by side
1/840,000 An average adult is about 840,000 times as tall as an E. coli bacterium is long. See side by side

Factors compare the length of an E. coli bacterium 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

The source presents these as rules of thumb and notes that laboratories do not always agree; size varies with strain and growth rate.
Volume and mass are converted exactly from the source's µm³ and pg because those units are not in the site's unit list.

Sources

Cell Biology by the Numbers (Milo and Phillips), How big is an E. coli cell and what is its mass?. Accessed 25 September 2026.

E. coli bacterium drawn to scale