Convert salinity measurements between Specific Gravity (SG), Parts Per Thousand (ppt or ‰), and Electrical Conductivity (EC in mS/cm or µS/cm). Assumes standard temperature (25°C/77°F).
Calculate Salinity
Salinity Unit Converter
Convert between common salinity measurement units: Specific Gravity (SG), Parts Per Thousand (ppt / ‰), and Electrical Conductivity (EC). Enter a value in one field to see the equivalent in others.
Note: Conversions involving Specific Gravity and Electrical Conductivity are temperature-dependent. This calculator assumes a standard reference temperature of **25°C (77°F)** and uses approximate formulas suitable for typical seawater/aquarium salinity ranges.
Enter Measurement & Convert
Understanding Salinity Units
Salinity measures the concentration of dissolved salts in water. It's crucial in oceanography, marine aquariums, and other fields. Common ways to express or measure salinity include:
- Parts Per Thousand (ppt or ‰): Represents grams of salt per kilogram of water (g/kg). This is a common unit for reporting salinity, roughly equivalent to g/L for typical seawater densities. Ocean water averages around 35 ppt.
- Specific Gravity (SG): A unitless ratio comparing the density of the sample water to the density of pure water at a specific temperature. Because dissolved salts increase water density, SG increases with salinity. It is heavily dependent on temperature. Common target for reef tanks is 1.025-1.026 SG.
- Electrical Conductivity (EC): Measures how well water conducts electricity, which increases as more salts (ions) are dissolved. It is measured in Siemens per meter (S/m), but more commonly milliSiemens per centimeter (mS/cm) or microSiemens per centimeter (µS/cm). EC is also very temperature-dependent. Standard seawater (35 ppt) has an EC of about 53 mS/cm at 25°C.
- Practical Salinity Units (PSU): The standard oceanographic unit, technically dimensionless. It's based on conductivity measurements relative to a standard KCl solution under controlled conditions (PSS-78 standard). For most purposes, PSU is numerically very close to ppt (‰).
Temperature Dependency & Approximations
Both Specific Gravity and Electrical Conductivity change significantly with water temperature. Accurate conversions require knowing the temperature at which the measurement was taken. This calculator simplifies things by assuming all measurements and conversions are relative to a standard temperature of **25°C (77°F)** and uses common approximations suitable for aquarium/seawater ranges:
PPT ≈ (SG@25°C - 1.000) / 0.00076PPT ≈ EC(mS/cm @25°C) * 0.67
Always use measurement devices calibrated for the correct temperature or use temperature compensation features if available.
Examples with Step-by-Step Solutions (@ 25°C)
Click on each example to see the conversion breakdown using the approximate formulas:
Example 1: Convert 35 ppt
Given: Salinity = 35 ppt
Steps (Approx. @ 25°C):
- To SG: SG ≈ 1.000 + (PPT * 0.00076) = 1.000 + (35 * 0.00076) = 1.000 + 0.0266 = 1.0266
- To EC (mS/cm): EC_mS ≈ PPT / 0.67 = 35 / 0.67 ≈ 52.24 mS/cm
- To EC (µS/cm): EC_µS = EC_mS * 1000 ≈ 52.24 * 1000 = 52240 µS/cm
Result: 35 ppt ≈ 1.0266 SG ≈ 52.2 mS/cm ≈ 52240 µS/cm
Example 2: Convert 1.026 SG
Given: Specific Gravity = 1.026
Steps (Approx. @ 25°C):
- To PPT: PPT ≈ (SG - 1.000) / 0.00076 = (1.026 - 1.000) / 0.00076 = 0.026 / 0.00076 ≈ 34.21 ppt
- To EC (mS/cm): EC_mS ≈ PPT / 0.67 ≈ 34.21 / 0.67 ≈ 51.06 mS/cm
- To EC (µS/cm): EC_µS = EC_mS * 1000 ≈ 51.06 * 1000 = 51060 µS/cm
Result: 1.026 SG ≈ 34.2 ppt ≈ 51.1 mS/cm ≈ 51060 µS/cm
Example 3: Convert 53 mS/cm
Given: EC = 53 mS/cm
Steps (Approx. @ 25°C):
- To PPT: PPT ≈ EC_mS * 0.67 = 53 * 0.67 ≈ 35.51 ppt
- To SG: SG ≈ 1.000 + (PPT * 0.00076) ≈ 1.000 + (35.51 * 0.00076) ≈ 1.000 + 0.02699 ≈ 1.0270
- To EC (µS/cm): EC_µS = EC_mS * 1000 = 53 * 1000 = 53000 µS/cm
Result: 53 mS/cm ≈ 35.5 ppt ≈ 1.0270 SG ≈ 53000 µS/cm
Example 4: Convert 45000 µS/cm
Given: EC = 45000 µS/cm
Steps (Approx. @ 25°C):
- To EC (mS/cm): EC_mS = EC_µS / 1000 = 45000 / 1000 = 45 mS/cm
- To PPT: PPT ≈ EC_mS * 0.67 = 45 * 0.67 ≈ 30.15 ppt
- To SG: SG ≈ 1.000 + (PPT * 0.00076) ≈ 1.000 + (30.15 * 0.00076) ≈ 1.000 + 0.0229 ≈ 1.0229
Result: 45000 µS/cm ≈ 45 mS/cm ≈ 30.2 ppt ≈ 1.0229 SG
Example 5: Convert 10 ppt (Brackish)
Given: Salinity = 10 ppt
Steps (Approx. @ 25°C):
- To SG: SG ≈ 1.000 + (10 * 0.00076) = 1.000 + 0.0076 = 1.0076
- To EC (mS/cm): EC_mS ≈ 10 / 0.67 ≈ 14.93 mS/cm
- To EC (µS/cm): EC_µS ≈ 14.93 * 1000 = 14930 µS/cm
Result: 10 ppt ≈ 1.0076 SG ≈ 14.9 mS/cm ≈ 14930 µS/cm
Example 6: Convert 40 ppt (Higher Salinity)
Given: Salinity = 40 ppt
Steps (Approx. @ 25°C):
- To SG: SG ≈ 1.000 + (40 * 0.00076) = 1.000 + 0.0304 = 1.0304
- To EC (mS/cm): EC_mS ≈ 40 / 0.67 ≈ 59.70 mS/cm
- To EC (µS/cm): EC_µS ≈ 59.70 * 1000 = 59700 µS/cm
Result: 40 ppt ≈ 1.0304 SG ≈ 59.7 mS/cm ≈ 59700 µS/cm
Example 7: Convert 1.025 SG
Given: Specific Gravity = 1.025
Steps (Approx. @ 25°C):
- To PPT: PPT ≈ (1.025 - 1.000) / 0.00076 = 0.025 / 0.00076 ≈ 32.89 ppt
- To EC (mS/cm): EC_mS ≈ 32.89 / 0.67 ≈ 49.10 mS/cm
- To EC (µS/cm): EC_µS ≈ 49.10 * 1000 = 49100 µS/cm
Result: 1.025 SG ≈ 32.9 ppt ≈ 49.1 mS/cm ≈ 49100 µS/cm
Example 8: Convert 50 mS/cm
Given: EC = 50 mS/cm
Steps (Approx. @ 25°C):
- To PPT: PPT ≈ 50 * 0.67 = 33.5 ppt
- To SG: SG ≈ 1.000 + (33.5 * 0.00076) ≈ 1.000 + 0.02546 ≈ 1.0255
- To EC (µS/cm): EC_µS = 50 * 1000 = 50000 µS/cm
Result: 50 mS/cm ≈ 33.5 ppt ≈ 1.0255 SG ≈ 50000 µS/cm
Example 9: Convert 1500 µS/cm (Low EC)
Given: EC = 1500 µS/cm
Steps (Approx. @ 25°C):
- To EC (mS/cm): EC_mS = 1500 / 1000 = 1.5 mS/cm
- To PPT: PPT ≈ 1.5 * 0.67 ≈ 1.005 ppt
- To SG: SG ≈ 1.000 + (1.005 * 0.00076) ≈ 1.000 + 0.00076 ≈ 1.0008
Result: 1500 µS/cm ≈ 1.5 mS/cm ≈ 1.0 ppt ≈ 1.0008 SG
Example 10: Convert 1.030 SG
Given: Specific Gravity = 1.030
Steps (Approx. @ 25°C):
- To PPT: PPT ≈ (1.030 - 1.000) / 0.00076 = 0.030 / 0.00076 ≈ 39.47 ppt
- To EC (mS/cm): EC_mS ≈ 39.47 / 0.67 ≈ 58.92 mS/cm
- To EC (µS/cm): EC_µS ≈ 58.92 * 1000 = 58920 µS/cm
Result: 1.030 SG ≈ 39.5 ppt ≈ 58.9 mS/cm ≈ 58920 µS/cm
Frequently Asked Questions (FAQs)
What salinity level should my reef aquarium be?
Most reef aquariums aim for levels similar to natural seawater, typically around 35 ppt, which corresponds to approximately 1.026 Specific Gravity (SG) at 25°C (77°F) or 53 mS/cm (53,000 µS/cm) Electrical Conductivity (EC) at 25°C.
How does temperature affect SG and EC readings?
As water temperature increases, its density decreases (lowering SG for the same salinity), while its electrical conductivity increases. This is why temperature compensation is important for accurate measurements using SG (hydrometer/refractometer) or EC meters. This calculator assumes 25°C.
Is PPT (‰) the same as g/L?
Not exactly, but they are very close for typical seawater densities. PPT (parts per thousand) is technically a mass ratio (grams of salt per kilogram of solution, g/kg). Grams per liter (g/L) is mass per volume. Since 1 liter of seawater weighs slightly more than 1 kg (e.g., about 1.025 kg at 35 ppt), 35 ppt is roughly 35.9 g/L. However, they are often used interchangeably in less precise contexts.
What are PSU (Practical Salinity Units)?
PSU is the standard unit in oceanography, defined by the water's conductivity relative to a standard solution (PSS-78). It is technically unitless. Numerically, PSU values are very close to PPT (‰) values for seawater.
My refractometer reads SG or PPT. Can I convert to EC?
Yes, this tool allows you to enter your SG (ensure it's temperature-compensated or measured near 25°C/77°F) or PPT reading to get an *estimated* EC value in mS/cm or µS/cm, assuming the standard temperature and typical seawater ion ratios, using approximate conversion factors.
