If Million is 'M' and Billion is 'B', Why is Thousand 'K'?

‘M’ is used for millions. ‘B’ is used for billions. Then why is thousand symbolized as ‘K’ and not ‘T’? Most of us might be using ‘K’ to write 1,000, especially when it comes to money (Rs 100K), marathons (5K) or follower count (50K), but how many of us know why ‘K’ denotes thousand?

Origins of ‘K’

The ‘K’ originates from the Greek word ‘khilioi’ (χίλιοι), meaning ‘thousand’. This Greek prefix became standardised in the metric system as ‘kilo-‘, where it represents 1,000 of something (e.g., kilogram or kilometre). The ‘K’ for thousand even appears in ancient texts, such as the Bible.

The French later shortened ‘khilioi’ to ‘kilo’, which is how terms like kilometre and kilogram came into the world. Since a kilogram is 1,000 grams, the symbol for a thousand became ‘K’.

Soon, the abbreviated form ‘K’ gained widespread use because it’s shorter and more convenient than writing out ‘1,000’, particularly in financial and technical contexts. The practice became even more common with the rise of computing and digital communication, where concise notation is valued.

Here’s how it developed across different periods and fields:

• Ancient Origins: The Greeks used ‘χ’ (chi) as shorthand for 1,000 in their numeral system. The Roman numeral ‘M’ was also used to represent 1,000.
• Scientific Standardisation (18th-19th centuries): The metric system was developed during the French Revolution and ‘kilo-‘ was officially adopted as a standard prefix in 1795. Scientists globally began using ‘k’ for consistency in measurements.
• Financial Industry (20th century): Stock markets and financial reports adopted ‘K’ to save space in sheets. ‘$10K’ became the standard shorthand for ‘$10,000’. Investment documents popularised terms like ‘401(k)’.
• Computing Era (Late 20th century): Computer science adopted ‘K’ for 1,024 bytes (kilobyte). This created some confusion as a computer ‘K’ isn’t exactly 1,000. Eventually this led to new terms (KiB for 1,024, KB for 1,000).
• Modern Digital Culture: Social media character limits encouraged shorter notation. ’10K followers’ became common parlance. The symbol gained new meanings (e.g., “10K race” for 10 kilometre run).
• International Usage: While ‘K’ is common in English, different notations exist in different regions. Some countries ‘M’ is used for thousand (from ‘mil’). In India, ‘1,000’ is often written as ‘1k’ or ‘1K’, while larger numbers follow traditional Indian terms like lakhs and crores.