CALCULATOR · SALINITY
Salinity converter: SG ↔ ppt ↔ conductivity
The short answer
Reef tanks target 35 ppt salinity, which equals a specific gravity of 1.0264 and a conductivity of 53.0 mS/cm at 25°C. The reef range is 33–36 ppt (1.025–1.027 SG). Every 1 ppt is about 0.00075 SG and 1.4 mS/cm.
The ReefRig Salinity Method
Anchor everything to 35 ppt = 1.0264 SG = 53.0 mS/cm at 25°C. Reef range is 33–36 ppt (1.025–1.027 SG); calibrate refractometers with 35 ppt fluid and correct for temperature.
35 ppt = 1.0264 SG = 53.0 mS/cm at 25°C — the reef standard.
Salinity conversion table (25°C)
Specific gravity, ppt (salinity) and conductivity for reef saltwater, referenced to 25°C. Aim for the 33–36 ppt band; 35 ppt is natural seawater and the safe default for corals.
| Salinity (ppt) | Specific gravity | Conductivity (mS/cm) |
|---|---|---|
| 28 | 1.0211 | 43.2 |
| 30 | 1.0226 | 46.0 |
| 31 | 1.0234 | 47.4 |
| 32 | 1.0241 | 48.8 |
| 33 | 1.0249 | 50.2 |
| 34 | 1.0256 | 51.6 |
| 35 | 1.0264 | 53.0 |
| 36 | 1.0272 | 54.4 |
| 37 | 1.0279 | 55.8 |
| 38 | 1.0287 | 57.2 |
Anchored to the universal reference 35 ppt = 1.0264 SG = 53.0 mS/cm at 25°C (standard oceanographic conversion). Specific gravity is temperature-dependent — calibrate refractometers with 35 ppt / 53 mS/cm standard fluid and correct for sample temperature.
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Convert a reading
Pick the meter you used, enter your reading, and read the other two units. Values are referenced to 25°C — correct for temperature if your sample is warmer or cooler.
Values referenced to 25°C. Specific gravity shifts with temperature, so calibrate a refractometer with 35 ppt fluid and take readings at tank temperature for the tightest accuracy.