“If all the world's bacteria were stacked on top of each other, the resulting column would stretch approximately 10 billion light-years.”

The result of the calculation is that the best estimate of the number of bacteria and archaea on Earth is about 3 × 1031, and the best estimate of the virus number is barely more than 10^31. Taken together, the low bound of the number of prokaryotes on Earth was estimated as 4 × 10^30.

Recent studies have estimated a staggering range of species numbers for bacteria, from low millions [6], to hundreds of millions , to low trillions [3]. All were based on extrapolations from molecular studies.

The number of microbial cells in the waters of the planet has been calculated to be in the range of 10^30 with a mass equal to the weight of 240 billion African elephants [13]. At any one time there are roughly five million trillion trillion (10^30) living bacteria and 10^31 phages (viruses that infect bacteria) that attack them, killing 40% of them every day [4–6].

The group, led by microbiologist William B. Whitman, estimates the number to be five million trillion trillion -- that's a five with 30 zeroes after it. If each bacterium were a penny, the stack would reach a trillion light years.

Using these different methods, the average length of the rod-shaped bacterium E. coli was determined to lie between 1.6 and 3.1 µm [12], [13], the average width was determined as 0.7–1.1 µm [11], [14] and the volume was determined to range from 0.5–4 µm3 [10], [15], [16], [17].

The sum of the biomass across all taxa on Earth is estimated to be about 550 Gt C, of which: ≈80% (≈450 Gt C) are plants [10]; ≈15% (≈70 Gt C) are bacteria, the second major component of biomass ; the remainder is due to other groups; in descending order: fungi (≈12 Gt C), archaea (≈8 Gt C), protists (≈4 Gt C), animals (≈2 Gt C) and viruses (≈0.2 Gt C).

An average-size bacterium—such as the rod-shaped Escherichia coli, a normal inhabitant of the intestinal tract of humans and animals—is about 2 micrometers (μm; millionths of a meter) long and 0.5 μm in diameter, and the spherical cells of Staphylococcus aureus are up to 1 μm in diameter.

Number of cells of bacteria and archaea estimated to inhabit Earth ; ~10^30 cells · Biosphere · Locey KJ, Lennon JT. Scaling laws predict global microbial diversity.

All the world's bacteria stacked on top of each other would stretch for 10 billion light-years. Together, Earth's 0.001mm-long microbes could wrap around the Milky Way over 20,000 times.

An average-size bacterium—such as the rod-shaped Escherichia coli, a normal inhabitant of the intestinal tract of humans and animals—is about 2 micrometers (μm; millionths of a meter) long and 0.5 μm in diameter, and the spherical cells of Staphylococcus aureus are up to 1 μm in diameter.

Most bacterial size range from 0.2 to 2.0 μm in diameter and 2 to 8 μm in length. The ubiquitous Escherichia coli is about 1 μm in diameter and 1-2 μm long.

The biggest area of uncertainty in species estimates is for bacteria and archaea. This can range from mere thousands to billions. A 2017 paper by Larsen et al. estimates that there are 1 to 6 billion species on Earth, and bacteria make up 70% to 90% of them.

The Earth contains an estimated one trillion species of microbes — with 99.999% of them remaining undiscovered.

A “rule of thumb” based upon generations of light and electron microscopy measurements for the dimensions of an E. coli cell is to assign it a diameter of about ≈1µm, a length of ≈2µm, and a volume of ≈1µm3 (1 fL). One of the simplest routes to an estimate of the mass of a bacterium is to exploit the ≈1 µm3 volume of an E. coli cell and to assume it has the same density as water. This naïve estimate results in another standard value, namely, that a bacterium such as E. coli has a mass of ≈1 pg (pico=10-12).

There are five nonillion bacteria in the Earth's ecosystem, including the ones found in living beings. That is 5 x 10 on 30th power. ... If we stack all the bacteria on top of each other, they would create a line that would be a trillion light years away from Earth.

The average diameter of spherical bacteria is 0.5-2.0 µm. For rod-shaped or filamentous bacteria, length is 1-10 µm and diameter is 0.25-1.0 µm. E. coli, a bacillus of about average size is 1.1 to 1.5 µm wide by 2.0 to 6.0 µm long.

Most bacteria fall within a size range of about 0.5 to 5 micrometers (µm) in length. To put this into perspective, one micrometer is one-millionth of a meter! If we think about it in more relatable terms, that's roughly equivalent to 1/100th the width of a human hair.

Based on an estimated total of 5 x 10^30 bacteria on Earth and an average bacterium length of 2 micrometers (2 x 10^-9 kilometers), the total length if all bacteria were stacked end-to-end would be approximately 1 x 10^22 kilometers. Converting this to light-years (where 1 light-year is approximately 9.461 x 10^12 kilometers), the resulting column would stretch about 1.057 billion light-years. This is significantly less than the claimed 10 billion light-years.

A light year, abbreviated ly, is the distance light travels in one year: roughly 9.46 × 10^12 kilometres (9.46 petametres, or about 5.88 × 10^12 (nearly six trillion) miles). More specifically, a light year is defined as the distance that a photon would travel, in free space and infinitely far away from any gravitational or magnetic fields, in one Julian year (365.25 days of 86400 seconds each).

The average size of bacteria is 0.2μm in diameter and 2−8μm in length. This is just the average size though. Sizes of bacteria can vary widely, with diameters ranging from 0.2μm to 2.0 μm.

If you took all of the world's bacteria, which are around 0.01 mm long, then stacked them on top of each other, they'd wrap around the entire Milky Way galaxy over 20,000 times, which would take you over 10 billion years to travel if you were moving at the speed of light.