The highest prefix allowed by the International System of Units (SI) is the “yotta”, for 24 zeroes

Scientists are lobbying for a new word to help them describe numbers larger than 1,000,000,000,000,000,000,000,000,000, amid concerns that the current system of units is insufficient.   A campaign for “hella” to join the likes of “kilo”, “mega” and “giga” as an internationally accepted prefix is attracting growing support. 


More than 20,000 scientists, students and members of the public have signed an online petition backing the new quantity, which would be used for figures with 27 zeros after the first digit.

Currently the highest prefix allowed by the International System of Units (SI) is the “yotta”, for 24 zeroes.

Austin Sendek, the physics student at the University of California who started the campaign, said that recent scientific developments required that the scales of measurement be extended.

“The analysis of many physical phenomena reveals natural quantities in excess of 27 orders of magnitude, a number which is currently ignored by the SI system,” he wrote on the Facebook petition outlining the case for the hella.

“Designating a prefix for 10^27 is of critical importance for scientists in all fields. This number is significant in many crucial calculations, including the wattage of the sun, distances between galaxies, or the number of atoms in a large sample.”

The amount of energy released by the Sun would be more elegantly expressed as 0.3 hellawatts than as 300 yottawatts, he added.

Hella is North Californian slang for “very” or “a lot of”. Mr Sendek and his supporters argue that its adoption would be a fitting honor for the state’s impressive record of scientific research.

If the change is approved, the hella would be the first new SI prefix introduced since 1991, when the International Committee for Weights and Measures approved yotta and zetta (21 zeroes).

Mr Sendek has already contacted the British chemist who heads the Consultative Committee for Units (CCU), the body which advises the international committee, in the hope of building support.

Professor Ian Mills of the University of Reading has promised to raise the petition at the next meeting of the CCU in September but said it was unlikely that the hella would win approval – for now.

He told the Telegraph: “The prefixes we introduced 20 years ago are still not widely used. There is no point making changes that nobody pays any attention to and would only make things more complicated.

“At the moment we are focusing on more pressing issues, such as redefining the weight of the kilogram. But he is correct to say that we will need prefixes to express a greater range of magnitudes as science advances. The very fact that a student is asking a question like this is very encouraging.”

In a letter to Mr Sendek he added: “I will mention this exchange at our next CCU meeting, and I am sure it will be received with smiles – but I doubt that it will go further!”

Prof Mills suggested that a simpler option would be for the committee to relax rules banning compound prefixes, so that, for instance, a hella could be expressed as a kiloyotta.

Even if the need for a new prefix was accepted, there is little chance it would take the name hella, he added. Most existing SI prefixes are derived from Latin or Greek words for numbers, a trend that the committee is keen to continue.


10 = deca

100 = hecto

1,000 = kilo

1,000,000 = mega

1,000,000,000 = giga

1,000,000,000,000 = tera

1,000,000,000,000,000 = peta

1,000,000,000,000,000,000 = exa

1,000,000,000,000,000,000,000 = zetta

1,000,000,000,000,000,000,000,000 = yotta


Via Telegraph