Salinity Converter
Convert water salinity between ppt, PSU, specific gravity, and conductivity (mS/cm).
For reef aquariums, marine tanks, brewing, and oceanography calculations.
Type in any field — the others update instantly. Values are approximate at 25°C.
Salinity measures the dissolved salt content in water.
Common units:
- ppt (parts per thousand): grams of salt per kilogram of water
- PSU (Practical Salinity Units): dimensionless, numerically equal to ppt
- Specific Gravity (SG): density compared to pure water (1.000)
- Conductivity (mS/cm): electrical conductivity at 25°C
Conversions (approximate):
- ppt ≈ PSU (for practical purposes, they are interchangeable)
- SG ≈ 1 + (ppt × 0.0008) (at 25°C)
- Conductivity ≈ ppt × 1.4118 mS/cm (approximate, varies with temperature)
Reference values:
| Water Type | ppt / PSU | Specific Gravity | Conductivity |
|---|---|---|---|
| Fresh water | 0–0.5 | 1.000 | 0–0.7 mS/cm |
| Brackish water | 0.5–30 | 1.000–1.024 | 0.7–42 mS/cm |
| Ocean water | 33–37 | 1.024–1.028 | 47–52 mS/cm |
| Reef aquarium | 34–36 | 1.025–1.027 | 48–51 mS/cm |
| Dead Sea | ~340 | ~1.240 | ~192 mS/cm |
These conversions are approximate. Exact values depend on temperature, pressure, and ionic composition.
The unit you reach for depends on what you’re doing. Oceanographers and lab work use PSU, which is derived from conductivity and is what modern instruments actually measure. Aquarists tend to think in specific gravity, because the cheap swing-arm hydrometer reads it directly, while ppt is the plain grams-of-salt-per-kilogram figure most people find intuitive. They’re close cousins: seawater sits near 35 ppt, 35 PSU, and 1.025 specific gravity all at once.
Specific gravity is the one to be careful with, because it shifts with temperature. A hydrometer calibrated for 25°C reads too high in a warm reef tank, which fools people into thinking the water is saltier than it is, so they over-dilute and stress the livestock. That’s exactly why serious reef keepers switch to a refractometer, which is far less temperature-sensitive and far more repeatable. Whatever tool you use, calibrate it and read at a consistent temperature; a salinity number without a known temperature is only half a measurement.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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