How Much Water Is on Earth?
The current USGS estimate for Earth’s total water volume is about 1.386 billion km³, or 332.5 million cubic miles. The figure of 326 million cubic miles comes from an older estimate used in mid-20th-century material; it is about 2% below the current estimate.
Converted to gallons, the USGS volume is about 366 quintillion U.S. gallons (3.66 × 10²⁰). The phrase “326 million trillion gallons” means 3.26 × 10²⁰ gallons mathematically and roughly matches the older volume, but “million trillion” is an unusual and potentially confusing phrasing. More than 96% of Earth’s water is in saline oceans.