Long and short scales

The long and short scales are two powers of ten number naming systems that are consistent with each other for smaller numbers, but are contradictory for larger numbers.^[1][2] Other numbering systems, particularly in East Asia and South Asia, have large number naming that differs from both the long and short scales. Such numbering systems include the Indian numbering system and Chinese, Japanese, and Korean numerals.^[1][2] Much of the remainder of the world adopted either the short or long scale. Countries using the long scale include most countries in continental Europe and most that are French-speaking, German-speaking and Spanish-speaking.^[3] Use of the short scale is found in most English and Arabic speaking countries and Brazil.

For powers of ten less than 9 (one, ten, hundred, thousand and million) the short and long scales are identical, but for larger powers of ten, the two systems differ in confusing ways. For identical names, the long scale grows by multiples of one million (10⁶), whereas the short scale grows by multiples of one thousand (10³). For example, the short scale billion is one thousand million (10⁹), whereas in the long scale, billion is one million million (10¹²). The long scale system includes additional names for interleaved values, typically replacing the word ending "-ion" by "-iard".

To avoid confusion, the International System of Units (SI) recommends using the metric prefixes to indicate magnitude. For example giga is always 10⁹ even though it's short scale billion and long scale milliard.