A marine tank can give two different numbers for the same water depending on whether you read a hydrometer or a refractometer. A hydrometer is built to read correctly only at one calibration temperature, so a reading taken at any other water temperature needs correcting. Enter your salinity and gravity readings, both temperatures and the coefficient from your hydrometer documentation, and this tool converts the salinity units, corrects the gravity and shows the gap to your target.
Unit conversion follows the definitions 1 ppt = 1 g/kg = 0.1 %, and the correction is corrected gravity = reading + coefficient x (water temperature - calibration temperature), with the formula printed in the results. The coefficient differs between hydrometers, so it is an input, and target salinity for marine keeping differs between references, so that is an input too (as of October 2026).
This tool does not convert between gravity and salinity. The relationship shifts with temperature and ionic makeup, so a single conversion formula would mislead. It also does not calculate how much salt mix to add, because product labeling differs. This tool is for reference only and does not replace veterinary care. Contact your veterinarian or an aquatic animal hospital right away if livestock close up or breathe rapidly.
Frequently Asked Questions
There is no single official figure, so this tool does not supply one. Enter the value from your own reference or your retailer.
Use the figure in your hydrometer documentation or from the maker. Entering 0 returns the reading unchanged.
No, that is not supported. The relationship depends on temperature and ionic makeup, so one fixed formula would carry a large error.