Exameter

What Is Exameter?

An exameter is a unit for measuring very large distances. It is used in science when distances are so huge that meters or kilometers are not big enough. One exameter is equal to one billion billion meters.

Definition

An exameter is a metric unit of length in the International System of Units, also called SI. It is built from the basic unit meter with the prefix exa.

1 exameter = 1 000 000 000 000 000 000 meters.

In scientific form this is written as:

• 1 exameter = 10¹⁸ meters
• 1 exameter = 1 000 000 000 000 000 kilometers = 10¹⁵ kilometers

This means an exameter is a million billion kilometers long.

History / Origin

The meter was created in France in the late 1700s as a standard way to measure length. Later, scientists needed special prefixes to show very big and very small amounts of meters.

The prefix exa was chosen for numbers equal to 10¹⁸, which is a 1 followed by 18 zeros. It comes from a Greek word that is linked to the number six, because 10¹⁸ is 1000 to the power of 6.

The prefix exa, and so the unit exameter, was officially accepted in the 1970s by the international group that manages the SI system. Since then exameter has been a correct SI unit name, but it is used almost only in advanced science.

Symbol & Abbreviation

Every SI unit has a short symbol.

• Name: exameter
• Symbol: Em

The symbol Em is made of:

• E – capital E for the prefix exa
• m – small m for meter

Important rules:

• Do not write EM or em for this unit. The correct symbol is Em.
• Write the number, then a space, then the symbol. Example: 2 Em.

Current Use Around the World

Exameters are not used in daily life. You will not see exameters on a road sign or in home building plans.

They are mainly used in:

• Astronomy – to talk about very large distances in space, such as between groups of stars or galaxies.
• Cosmology and physics – to describe the size of parts of the universe in theories and models.
• Scientific writing and teaching – when people want to show distances using SI units instead of special space units like light years or parsecs.

Even in these fields, scientists more often use light years, astronomical units, or parsecs. Exameter is useful mainly when someone wants to stay inside the metric SI system for very large distances.

Example Conversions

Here are some simple examples to help you feel how large an exameter is.

Exameters to meters

• 1 Em = 1 000 000 000 000 000 000 m
• 0.5 Em = 500 000 000 000 000 000 m
• 3 Em = 3 000 000 000 000 000 000 m

Exameters to kilometers

• 1 Em = 1 000 000 000 000 000 km
• 0.2 Em = 200 000 000 000 000 km
• 5 Em = 5 000 000 000 000 000 km

Exameters to light years (about values)

• 1 light year ≈ 9 460 000 000 000 000 m
• 1 Em ≈ 100 light years
• 0.5 Em ≈ 50 light years
• 2 Em ≈ 200 light years

Meters to exameters

• 1 000 000 000 000 000 000 m = 1 Em
• 500 000 000 000 000 000 m = 0.5 Em
• 10 000 000 000 000 000 000 m = 10 Em

Related Units

Exameters belong to the family of metric length units. Here are some related units, from smaller to larger:

• Meter (m) – base SI unit of length.
• Kilometer (km) – 1 000 m.
• Megameter (Mm) – 1 000 000 m.
• Gigameter (Gm) – 1 000 000 000 m.
• Terameter (Tm) – 10¹² m.
• Petameter (Pm) – 10¹⁵ m.
• Exameter (Em) – 10¹⁸ m.
• Zettameter (Zm) – 10²¹ m.
• Yottameter (Ym) – 10²⁴ m, even larger than zettameter.

Other space related distance units that are not simple metric units, but are often used with exameter size distances, include:

• Astronomical unit (AU) – about the average distance from Earth to the Sun.
• Light year (ly) – the distance light travels in one year.
• Parsec (pc) – a common unit in astronomy for very large distances.

FAQs

How big is an exameter compared to a kilometer?
An exameter is much larger than a kilometer. One exameter is one million billion kilometers, written as 1 000 000 000 000 000 km. So 1 Em = 10¹⁵ km.

Is exameter an official SI unit?
Yes. Exameter is an official SI unit formed by joining the SI prefix exa with the base unit meter. Its symbol is Em.

Where would I ever use exameters?
You would usually only see exameters in advanced science topics, such as astronomy, cosmology, or theoretical physics, when people talk about distances across large parts of the universe.

Why do scientists not use exameters all the time for space?
Scientists often prefer units like light years, astronomical units, or parsecs for space, because those units are easier to picture and match how objects move and orbit in space. Exameters are handy mostly when someone wants to stay inside the SI metric system.

Is exameter bigger than a light year?
Yes. One exameter is roughly equal to 100 light years. That means light would take about 100 years to travel across a distance of 1 Em.

How do I convert exameters to meters?
To change exameters to meters, multiply by 1 000 000 000 000 000 000. For example, 2 Em = 2 × 1 000 000 000 000 000 000 m = 2 000 000 000 000 000 000 m.

How do I convert meters to exameters?
To change meters to exameters, divide by 1 000 000 000 000 000 000. For example, 5 000 000 000 000 000 000 m ÷ 1 000 000 000 000 000 000 = 5 Em.

Is exameter the biggest metric length unit?
No. Zettameter (Zm) and yottameter (Ym) are even bigger metric length units, equal to 10²¹ m and 10²⁴ m.

Is exameter related to exabyte?
They both use the prefix exa, which means 10¹⁸, but they measure different things. Exameter measures length, while exabyte measures digital data. The prefix exa just tells you the size of the number.