How big is Largest Virus? | Scale of the Universe

The virus shown here, Pithovirus sibericum, is one of the largest viruses known, as of 2026. Its oval particles are typically about 1.5 micrometers long, measured from end to end. A micrometer is a millionth of a meter. Many common viruses are only about 0.1 micrometers across, so a Pithovirus particle is about 15 times as long as they are wide. Scientists described it in 2014, after reviving it from frozen ground in Siberia that is more than 30,000 years old.

Size

Pithovirus particles are shaped like stretched-out eggs, with a plug at one end that the researchers call a cork. When they were first measured with an electron microscope, the particles were about 1.5 micrometers long and 0.5 micrometers wide. That made Pithovirus larger than the pandoraviruses, the previous largest known viruses, whose particles are about 1 micrometer long.

The first measurements were made on particles that had been chemically preserved and sliced thin. In 2017, researchers froze whole particles and imaged them in a state closer to their natural one. Most measured 1.35–1.65 micrometers long and 0.75–0.85 micrometers wide. The smallest were about 0.9 micrometers long and the largest about 2.5 micrometers.

Particles this large can be seen with an ordinary light microscope. Pithovirus was first spotted that way, as oval particles multiplying in a laboratory culture.

Size comparisons

Many viruses are about 0.1 micrometers across, so a Pithovirus particle is about 15 times as long.
If a 0.1-micrometer virus were enlarged to the size of a tennis ball, about 6.7 centimeters (2.6 inches) across, a Pithovirus particle would be about 1 meter (3.3 feet) long.
A Pithovirus particle is about three-quarters the length of an E. coli bacterium, which is about 2 micrometers long.
It is about as long as a mitochondrion, the part of a cell that releases energy from food, which is 1–2 micrometers long.

Which virus is largest

The answer depends on what is measured and which reports are counted. Tupanvirus, described in 2018, has a head about 0.45 micrometers across attached to a long tail. Its particles average about 1.2 micrometers long, but some reach 2.3 micrometers because their tails vary in length.

In 2019, researchers reported spindle-shaped particles more than 4 micrometers long in electron microscope photos of arrow worms, small sea animals. They concluded that the particles are viruses, the longest ever reported. They also called for studies of the particles' genes to learn more about them.

Revived from permafrost

Pithovirus came from a sample of permafrost, permanently frozen ground, collected in 2000 in northeastern Siberia. The layer it came from is more than 30,000 years old, a date found by radiocarbon dating. Researchers mixed the sample into a culture of amoebas, single-celled organisms, and the virus began to multiply inside them.

The team chose amoebas because viruses that infect them are a safe way to test whether ancient viruses can still be infectious. They suggested that permafrost thawed by global warming, mining or drilling could one day release viruses harmful to people or animals.