Freezing Point Depression (Food) Calculator

Calculate freezing point depression from solute content and estimate ice fraction at storage temperature.

About this calculator

Freezing point depression tells you why food doesn't freeze at 0°C: dissolved solutes — sugars, salts, anything in solution — lower the point at which ice starts forming, following the same colligative-property math used for any solution: ΔTf = Kf × molality × the van't Hoff factor i, with Kf fixed at water's cryoscopic constant of 1.86°C·kg/mol. Molality here comes from dividing the solute mass by its average molecular weight to get moles, then dividing by the water mass in kilograms — so an accurate molecular weight matters as much as an accurate mass; sucrose (342), glucose (180), and salt (58.4, but with i≈2 for dissociation) give meaningfully different depressions for the same gram amount. Beyond the freezing point itself, the calculator estimates what fraction of the water is actually frozen solid at your chosen storage temperature, using a simplified Riedel/Chen-style approximation (ice fraction ≈ 1 − Tf/Ts) rather than a full phase diagram — treat it as a useful estimate of texture-relevant ice content, not a precise cryoscopic model.

As ice forms, the solutes concentrate into the remaining unfrozen water, and the calculator reports that effective concentration too, which is the real driver of freeze-concentration effects like grainy texture or accelerated enzymatic browning in frozen foods. A common mixup: this model assumes one dominant, well-characterized solute — a food with several solutes at different molecular weights needs either a weighted-average MW or per-solute calculations summed together.

Inputs

Solute mass (g)

Avg. solute MW (g/mol)

Water mass (g)

van't Hoff factor (i)

Storage temperature (°C)

°C

Tab to move between fields

Results

Freezing point (°C)

-0.27

Ice fraction (%)

98.49

ΔTf depression (°C)0.27

Molality (mol/kg)0.15

Moles of solute0.15

Unfrozen water (%)1.51

Conc. in unfrozen phase (%)76.8

Solute Mass Fraction0.05%

How to Use This Calculator

Enter the mass of dissolved solutes and their average molecular weight in g/mol.
Set the water mass in grams and the van't Hoff factor (1 for sugars, ~2 for NaCl).
Enter your freezer storage temperature in °C.
The calculator shows freezing point, ΔTf depression, molality, moles of solute, ice fraction at storage temperature, and effective solute concentration in unfrozen water.
Use ice fraction to predict product texture changes during frozen storage and optimize sugar/salt levels for desired freeze point.

How the result changes with Avg. solute MW (g/mol)

Avg. solute MW (g/mol)	Freezing point (°C)	Ice fraction (%)
171	-0.54	96.98
257	-0.36	97.99
513	-0.18	98.99
855	-0.11	99.4

What each input means

Solute mass (g): Total mass of dissolved solutes (sugars, salts, etc.) in grams.
Avg. solute MW (g/mol): Average molecular weight. Sucrose = 342, glucose = 180, NaCl = 58.4, fructose = 180.
Water mass (g): Mass of water (solvent) in the food in grams.
van't Hoff factor (i): Dissociation factor. 1 for sugars, ~2 for NaCl, ~3 for CaCl₂.
Storage temperature (°C): Freezer storage temperature to estimate ice fraction.

What each result means

Freezing point (°C): Predicted initial freezing point of the food product.
ΔTf depression (°C): Magnitude of freezing point depression below 0 °C.
Molality (mol/kg): Moles of solute per kilogram of water.
Moles of solute: Calculated moles of solute from mass and molecular weight.
Ice fraction (%): Estimated percentage of water that is frozen at the storage temperature.
Unfrozen water (%): Percentage of water remaining liquid at storage temperature.
Conc. in unfrozen phase (%): Effective solute concentration in the remaining unfrozen water.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Solute mass (g) = 50, Avg. solute MW (g/mol) = 342, Water mass (g) = 1000, van't Hoff factor (i) = 1 = 5 input(s) provided
Calculate Freezing point
Freezing point = 0 - deltaT
-0.272 = -0.272
Calculate Ice fraction
98.49 = 98.49
Calculate ΔTf depression
ΔTf depression = kf * molality * vanHoffFactor
0.272 = 0.272
Calculate Molality
0.1462 = 0.1462

Engine last updated September 1, 2026. Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does the calculator need molecular weight, not just the mass of dissolved solute?

Freezing point depression is a colligative property, meaning it depends on the number of dissolved particles (moles), not their mass. The calculator converts your solute mass to moles by dividing by molecular weight before computing molality, so the same 50 g of sucrose (MW 342) and salt (MW 58.4) produce very different molalities and very different freezing point depressions for an identical gram amount.

What does the van't Hoff factor do, and why is it 1 for sugar but roughly 2 for salt?

The van't Hoff factor (i) accounts for a solute dissociating into multiple particles in solution. Sugar molecules stay intact, so i = 1, but salt splits into a Na+ and a Cl- ion, roughly doubling its effective particle count and its freezing-point-lowering power, so i ≈ 2. The calculator multiplies molality directly by this factor in ΔTf = Kf × molality × i, so getting i wrong for an ionic solute understates the depression by close to half.

Why does the ice fraction estimate depend on the storage temperature I enter, not just the freezing point?

Food doesn't freeze all at once the way pure water does — as ice crystallizes out, the remaining unfrozen water gets more concentrated in solutes and its own freezing point keeps dropping. The calculator's ice-fraction estimate (1 - Tf/Ts) compares your chosen storage temperature to the predicted initial freezing point, so a colder freezer setting always yields a higher estimated ice fraction for the same formulation.

What does effective concentration in the unfrozen phase tell me that the initial solute concentration doesn't?

As ice forms, the solute mass doesn't change but it becomes dissolved in less liquid water, so its concentration in the remaining unfrozen fraction rises well above the original recipe concentration. The calculator computes this using the unfrozen water mass rather than total water mass, and that elevated concentration is the real driver of freeze-concentration effects like grainy ice-cream texture or accelerated enzymatic reactions in frozen produce.

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