About Hydrostat

Hydrostat is an independent project, built and maintained by a small team and supported by OceanWell. Last reviewed September 2026.

What this is

Hydrostat is a water unit converter for people who work with water supply: utility engineers, hydrologists, desalination and reuse project teams, regulators and students. It converts volume and flow quantities across the unit systems used in the United States, the United Kingdom, Europe, Australia and the Gulf.

Conversion factors

Every conversion runs through a single litre base, using the exact values in NIST Special Publication 811: 1 US gallon = 3.785411784 litres; 1 Imperial gallon = 4.54609 litres; 1 cubic foot = 28.316846592 litres; 1 acre-foot = 1,233,481.83754752 litres; 1 cubic metre = 1,000 litres; 1 megalitre = 1,000,000 litres; 1 gigalitre = 1,000 megalitres.

Flow units are derived from those same base values rather than entered separately: per second is the base volume × 86,400, per minute × 1,440, per hour × 24, per day the base volume itself, and per year the base volume ÷ 365. Per-year units use a 365-day year.

Rounding

Results display to three decimal places for values of 1 or more and four significant figures below 1, with thousands separators. Arithmetic is full double precision; only the display is rounded.

Data sources

Conversion factors follow NIST Special Publication 811 and the US Geological Survey water-science glossary. Capacity examples reference published figures from operators and project developers, such as the Carlsbad Desalination Plant (Poseidon Water), the Sorek plant (IDE Technologies) and OceanWell's subsea water farms; figures are attributed where they appear.

Relationship with OceanWell

Hydrostat is built and supported in partnership with OceanWell, and the pod visualisation uses OceanWell's published water-farm capacity figures. The conversion factors themselves are standards-based and independent of any project.

Corrections and citation

To report an incorrect factor or request a unit, email hello@hydrostat.net. Cite as: Hydrostat, "Water unit converter", hydrostat.net, accessed on the date of use.