User Rating 0.0 ★★★★★

Total Usage 0 times

Category Science & Math

Presets:

Input Mode:

Salt Mass (NaCl)

Water Amount

Concentration Value

Total Solution Mass (optional)

Measured Value

Solution Temperature

Results

⚠

Salinity (% w/w) —

Salinity (ppt / ‰) —

Salinity (g/L) —

Salinity (mg/L · ppm) —

Density (kg/m³) —

Specific Gravity —

Baumé (°Bé) —

Freezing Point —

Boiling Point —

Salt Mass in Solution —

Water Mass in Solution —

PSU (≈ ppt) —

Saturation Level

▼ ▼

0% Seawater 3.5% Eutectic 23.3% Sat. 26.3%

Is this tool helpful?

Your feedback helps us improve.

★ ★ ★ ★ ★

About

Miscalculating brine concentration leads to frozen pipelines, failed food preservation, and corroded infrastructure. A 2% error in salinity can shift freezing point by over 1°C, enough to burst a heat exchanger in sub-zero conditions. This calculator computes salinity as mass fraction S = m_saltm_salt + m_water and derives density, freezing point depression, boiling point elevation, specific gravity, and Baumé degrees using empirically validated polynomial models for NaCl solutions. Results are valid for concentrations from 0 to the eutectic point near 26.3% at 20°C. The density model approximates the UNESCO 1983 equation of state simplified for single-salt systems. Accuracy degrades for mixed-salt brines or concentrations approaching saturation.

Pro tip: industrial brine systems rarely operate above 23% NaCl because the eutectic freezing point at −21.1°C represents the minimum achievable temperature. Exceeding this concentration provides no additional freeze protection and risks crystallization in pumps and valves. Account for temperature when reading hydrometers. A Baumé reading at 15°C differs from one at 25°C by roughly 0.3 degrees due to thermal expansion of the solution.

Formulas

Salinity as mass fraction (weight percent):

S = m_saltm_salt + m_water × 100

where S = salinity in % w/w, m_salt = mass of dissolved NaCl, m_water = mass of water (solvent).

Brine density approximation (simplified polynomial for NaCl at temperature T):

ρ(S, T) ≈ ρ_w(T) + 7.0 ⋅ S + 0.0025 ⋅ S² − 0.004 ⋅ S ⋅ (T − 20)

where ρ_w(T) is pure water density at temperature T in °C, computed via the Kell formula: ρ_w ≈ 999.842 + 0.06794T − 0.009095T² + 0.0001002T³ − 1.12×10⁻⁶T⁴.

Freezing point depression for NaCl:

T_f ≈ −0.0621 ⋅ S_ppt

where S_ppt = salinity in parts per thousand. Valid below the eutectic concentration of 23.3%.

Boiling point elevation:

T_b ≈ 100 + 0.52 ⋅ S ÷ 58.44(1 − S ÷ 100) ⋅ 0.001

where 58.44 g/mol is the molar mass of NaCl and 0.52 °C⋅kg/mol is the ebullioscopic constant of water.

Baumé degrees (for liquids heavier than water):

°Bé = 145 − 145SG

where SG = specific gravity relative to pure water at the reference temperature.

Reference Data

NaCl Concentration (% w/w)	Density at 20°C (kg/m³)	Freezing Point (°C)	Boiling Point (°C)	Specific Gravity	Baumé (°Bé)	Salinity (ppt)
0 (Pure Water)	998.2	0.0	100.0	1.000	0.0	0
1	1005.3	−0.6	100.1	1.007	1.0	10
2	1012.5	−1.2	100.1	1.014	2.0	20
3.5 (Seawater)	1024.8	−2.0	100.2	1.025	3.6	35
5	1033.6	−3.1	100.3	1.035	5.1	50
7	1047.0	−4.4	100.4	1.049	7.0	70
10	1070.7	−6.6	100.6	1.071	10.0	100
12	1086.0	−8.0	100.7	1.088	12.2	120
15	1108.9	−10.9	100.9	1.111	15.4	150
18	1132.4	−13.8	101.1	1.134	18.3	180
20	1148.1	−16.5	101.3	1.150	20.4	200
23.3 (Eutectic)	1174.2	−21.1	101.5	1.176	23.6	233
25	1188.6	−9.3*	101.7	1.190	25.3	250
26.3 (Saturated)	1199.3	−1.2*	101.8	1.201	26.6	263

Frequently Asked Questions

Brine density decreases approximately 0.3 - 0.5 kg/m³ per 1°C increase. Hydrometers are calibrated at a reference temperature (typically 15.6°C or 20°C). Reading at a different temperature without correction can introduce errors of 0.5 - 1.0% in estimated concentration. This calculator accounts for temperature in its density polynomial. Always record the brine temperature alongside hydrometer readings for accurate field measurements.

The NaCl - water eutectic occurs at 23.3% concentration and −21.1°C. At this exact composition, the entire solution solidifies simultaneously. Adding more salt above 23.3% actually raises the freezing point because excess NaCl crystallizes out as NaCl⋅2H₂O (hydrohalite), effectively reducing the liquid-phase concentration. For freeze protection below −21°C, switch to CaCl₂ (eutectic at −51°C) or ethylene glycol.

For liquids denser than water: SG = 145 ÷ (145 − °Bé). Inversely, °Bé = 145 − 145 ÷ SG. This is the modulus-145 Baumé scale (US standard). Some older European instruments use modulus 144.3. Confirm which scale your hydrometer uses before comparing readings. This calculator uses the 145 modulus convention.

Practically, yes. The Practical Salinity Unit (PSU) is dimensionless and defined by conductivity ratio relative to standard KCl solution. For most NaCl brines, 1 PSU ≈ 1 ppt (g/kg). The difference matters in oceanographic precision work where mixed-salt composition affects conductivity differently than pure NaCl. For industrial NaCl brines, treating PSU and ppt as interchangeable introduces less than 0.1% error.

The linear freezing point depression model (T_f ≈ −0.0621 ⋅ S_ppt) assumes all salt remains dissolved. Above 23.3%, the solution is supersaturated at sub-zero temperatures. Salt precipitates as hydrohalite crystals, changing the effective liquid concentration. The phase diagram follows a different branch (liquidus of NaCl⋅2H₂O) where freezing point rises steeply. This calculator flags concentrations above the eutectic as a warning.

The polynomial model used here approximates measured NaCl solution densities within ±0.5 kg/m³ for concentrations 0 - 26% and temperatures 0 - 100°C. Full UNESCO equation of state precision (used in oceanography) requires 27 coefficients and multi-salt composition data. For CaCl₂, MgCl₂, or mixed brines, this model will give incorrect results. Use it for NaCl (table salt / rock salt / solar salt) solutions only.