Coolant Mixture Calculator
This coolant mixture calculator determines how many quarts or liters of antifreeze and distilled water to mix to achieve your target freeze protection temperature for ethylene glycol based coolant. Proper coolant mixture is critical for protecting the engine against freezing in winter, preventing boil-over in summer, and providing corrosion protection year-round. The freeze point data in this tool is based on the ASTM D3306 and SAE J1034 specifications for ethylene glycol engine coolant, which is the industry-standard formulation used in most vehicles worldwide.
Coolant mixture formulas
Antifreeze volume = Total volume * percentage / 100 Water volume = Total volume - Antifreeze volume Freeze point (F): 30% = -4F, 40% = -12F, 50% = -34F, 60% = -62F, 70% = -84F
Freeze point and boiling point data are based on ASTM D3306 ethylene glycol coolant tables. The boiling point shown is atmospheric; with a 15 psi pressure cap, add approximately 32 degrees F (18 degrees C) to the value shown.
Coolant mixture reference
- 30% antifreeze / 70% water: freeze point approximately -4 degrees F (-20 C). Adequate for mild climates.
- 40% antifreeze / 60% water: freeze point approximately -12 degrees F (-24 C). Minimum for most of the US.
- 50% antifreeze / 50% water: freeze point approximately -34 degrees F (-37 C). Standard recommendation.
- 60% antifreeze / 40% water: freeze point approximately -62 degrees F (-52 C). For severe climates.
- 70% antifreeze / 30% water: freeze point approximately -84 degrees F (-64 C). Maximum safe concentration.
Frequently asked questions
What ratio of antifreeze to water do I need?
A 50/50 mix of ethylene glycol antifreeze and water provides freeze protection to approximately -34 degrees F (-37 C) and is the standard recommendation for most climates. A 70/30 antifreeze/water mix (maximum recommended) protects to approximately -84 degrees F (-64 C). Never exceed 70% antifreeze as pure antifreeze actually has a higher freeze point than a 50/50 mix.
Why does pure antifreeze freeze at a higher temperature than a 50/50 mix?
Pure ethylene glycol freezes at 8.6 degrees F (-13 C). Mixing it with water creates a solution with a lower freeze point through freezing-point depression. The optimal freeze protection occurs around 60-70% antifreeze; beyond that, freeze protection decreases because you are removing the water needed for the colligative effect.
Does antifreeze ratio affect boiling point?
Yes. A 50/50 mix raises the boiling point to about 263 degrees F (128 C) at atmospheric pressure vs 212 F for pure water. The pressurized cooling system (typically 15-18 psi cap) further raises this to approximately 265-268 degrees F. Higher antifreeze concentrations continue to raise the boiling point.
How do I check my current coolant mixture?
Use a coolant hydrometer or optical refractometer to test the mixture strength. Hydrometers use float balls to indicate freeze protection; refractometers use the light-bending property of glycol solutions for a more precise reading. Test annually or at every coolant change.
How much coolant does a car hold?
Most passenger cars and light trucks hold 1.5 to 3 gallons (6 to 12 liters) of coolant in the complete cooling system. Check your owner's manual for the exact capacity before mixing a batch of coolant.
Official sources
- SAE International J1034: sae.org - engine coolant specifications and test methods.
- ASTM International D3306: astm.org - ethylene glycol base engine coolant standard.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.