How we calculate

Every number has a source

Each reference object (a bathtub, the Hoover Dam's yearly output) has one or more measured values. Every value records where it came from and when it was checked. Those sources are listed at the bottom of every article and on each object's page.

The arithmetic

To compare two things, both values are converted to the same unit (litres, metres, kilograms, kilowatt-hours and so on) and divided. The calculation is done by the site's own code, never estimated by hand or by AI.

Rounding

Exact ratios like 11,793.4 are hard to remember, so we round:

• Between 1 and 10: to one decimal place (2.5).
• 10 and above: to two significant figures (18,000).
• A million and above: in words (16 million, 2.4 billion).
• Less than one: as a fraction (1/40).

When rounding changes a number, we say "about". The exact ratio is shown under each comparison.

Corrections

Sources are rechecked at least once a year. When a figure changes, every comparison that uses it is recalculated automatically.