Antifreeze Mix Calculator

Written byOleh Soloninupdated 25 September 2026

What to work out

System volume, l

Freezing point wanted, °C

From 0 down to −45 °C: that is where the sources' data ends.

Result

Concentrate, l3.09
Distilled water, l2.91
Concentrate share, %51.5%
Freezes at, °C-35
Boils at, °C112
What matters
Mix with distilled water only: tap-water salts leave scale and sediment.

More concentrate is not better

Works out the concentrate and distilled water needed for a coolant with the freezing point you want, and gives the boiling point of the resulting mixture.

The freezing point of ethylene glycol in water depends on how much glycol there is. The calculator takes it from Lange's Handbook as reproduced on the English Wikipedia's "Ethylene glycol (data page)": 30% by volume freezes at −12.8 °C and 50% at −33.2 °C. For 60% it uses −45 °C from the article "Ethylene glycol". The data page heads that row in °F, although the values match Celsius tables, and other sources put a 50% mix nearer −37 °C — so treat the result as an estimate and follow the coolant maker's dilution chart.

The sources disagree by a few degrees: "Antifreeze" gives about −37 °C for a 1:1 mix and the Russian article on ethylene glycol −40 °C. The calculator sticks to the warmest figures, so it recommends concentrate with a margin. It stops at 60%: the data runs out there, and "Antifreeze" notes that mixtures rarely go stronger.

How to use

Choose whether you are mixing from scratch or strengthening what is already in the system.
Enter the cooling-system volume and the freezing point you want, from 0 down to −45 °C.
To strengthen, enter the current concentrate share — a hydrometer or refractometer will tell you.
Read the concentrate and water to mix, or how much mixture to drain and replace with concentrate.

Concentrate share by freezing point

Each row is a separate run of the calculator for a 6-litre system. Values between the handbook's points are interpolated in a straight line.

Every row comes from the calculator on this page.
Freezes at	Glycol share	Concentrate	Water	Boils at
−15 °C	33.3%	2 l	4 l	108 °C
−25 °C	43.6%	2.62 l	3.38 l	110 °C
−30 °C	47.5%	2.85 l	3.15 l	111 °C
−35 °C	51.5%	3.09 l	2.91 l	112 °C
−40 °C	55.8%	3.35 l	2.65 l	113 °C
−45 °C	60%	3.6 l	2.4 l	115 °C

Strengthening a mixture already in the car

A full system has no room to top up, so some mixture is drained and replaced with concentrate. The drained mixture takes glycol with it, which means more has to be swapped than the difference in shares: volume × (target − current) ÷ (100 − current).

For 6 litres and −35 °C: from 30% swap 1.85 l, from 40% swap 1.15 l. If the current share is already enough — 50% for a −25 °C target, say — the calculator says so.

What this calculator shows

Concentrate and water for your system
The resulting glycol share and freezing point
The mixture's boiling point at atmospheric pressure

What to keep in mind

Concentrate is treated as pure ethylene glycol. Retail concentrates also carry additives, so for a particular product the label's ratio is the one to follow.
The boiling point is at atmospheric pressure, from the vapour–liquid table on the same data page; in a pressurised system it is higher.

FAQs

What ratio should I mix antifreeze concentrate at?

It depends on the target: on the calculator's reference data 50% concentrate gives −33.2 °C, 55.8% gives −40 °C and 60% gives −45 °C. For a retail product with additives, the maker's label gives the exact ratio.

Can I pour concentrate in neat?

No. Pure ethylene glycol freezes at −12.9 °C, and its specific heat capacity is about half that of water, so the system sheds heat less well.

What water should I use?

Distilled. The hardness salts in tap water settle as scale inside the cooling jacket and the radiator.

How much concentrate strengthens an existing mix?

Drain some mixture and replace it with the same volume of concentrate: volume × (target − current) ÷ (100 − current). For 6 l going from 30% to −35 °C, that is 1.85 l.

Why do different charts give different figures?

The sources disagree: for a 1:1 mix Lange's Handbook gives −33.2 °C, the English "Antifreeze" article about −37 °C, the Russian article on ethylene glycol −40 °C. The calculator takes the warmest, so its concentrate share runs higher than most charts on bottles.

Can I mix coolants of different colours?

The colour is a dye added so the fluid is easy to identify. Compatibility comes from the additive package, so mix only what the maker's specification allows.

Worked example

Six litres for −35 °C

Input: 6 l, −35 °C

Output: 3.09 l of concentrate and 2.91 l of water, 51.5% glycol

Note: By the vapour–liquid equilibrium table in Lange's Handbook, the mix boils at about 112 °C unpressurised; coolant makers quote a few degrees less, so use your own coolant's figure. If the system already holds 30% glycol, draining 1.85 l and replacing it with concentrate is enough: 6 × (51.5 − 30) ÷ (100 − 30).

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