I understand million and billion, but what comes after trillion?

[John]

I understand million and billion, but what comes after trillion? And what’s the difference between the US and UK naming systems?

[Konstantin]

The Names of Large Numbers calculator/reference shows the naming convention and the difference between systems. In the US (short scale) system: thousand = 10^3, million = 10^6, billion = 10^9, trillion = 10^12, quadrillion = 10^15, quintillion = 10^18, sextillion = 10^21, septillion = 10^24, octillion = 10^27, nonillion = 10^30, decillion = 10^33. The pattern: each new name multiplies by 1000. In the traditional UK (long scale) system, which most of Europe uses: million = 10^6, milliard = 10^9 (US billion), billion = 10^12 (US trillion), billiard = 10^15, trillion = 10^18 (US quintillion). Pattern: each new -illion multiplies by a million. This creates huge confusion! “Billion” means different things: US billion = 10^9, old UK billion = 10^12 (1000x larger!). Modern UK now mostly uses short scale to match US. Real-world context: US national debt is ~$30+ trillion ($30×10^12), world GDP is ~$100 trillion, grains of sand on Earth ? 7.5 sextillion (7.5×10^21), atoms in human body ? 7 octillion (7×10^27), atoms in observable universe ? 10^80 (no standard name, sometimes called “ten duovigintillion”). For writing: use scientific notation for clarity (3×10^24 is clearer than “3 septillion”), use metric prefixes when appropriate (giga=10^9, tera=10^12, peta=10^15), be explicit about which system you’re using in international contexts. Fun fact: Googol = 10^100, Googolplex = 10^googol = 10^(10^100)!

• This reply was modified 2 days, 11 hours ago by  Konstantin.