Calculate antifreeze-to-water ratios, refill amounts, and final mix percentages for coolant systems in gallons, liters, quarts, and more.
Antifreeze Ratio Formula
The antifreeze ratio is the antifreeze volume divided by the total coolant volume. The calculator uses this relationship to solve for percentage, antifreeze volume, or total coolant volume.
Ratio Solver
P = A/T * 100
A = T * P/100
T = A/(P/100)
Full Refill With Concentrate
A = C * P/100
W = C - A
Full Refill With 50/50 Premix
Fill = C
P_final = 50
Partial Drain and Refill
A_final = C*(P_current/100) - D*(P_current/100) + D*R
P_final = A_final/C * 100
- P = antifreeze percentage
- A = antifreeze volume
- T = total coolant volume
- C = cooling system capacity
- W = distilled water volume
- D = volume drained
- R = antifreeze fraction of the refill fluid, where concentrate is 1, 50/50 premix is 0.5, and water is 0
- A_final = antifreeze volume after draining and refilling
- P_final = final antifreeze percentage after refilling
The ratio solver works when you enter exactly two of the three values: total coolant volume, antifreeze percentage, and antifreeze volume. The full refill mode assumes the cooling system is empty and tells you how much concentrate and water to add. The partial drain mode assumes the coolant you remove has the same mixture as the coolant remaining in the system.
Common Antifreeze Mix Targets
| Antifreeze Percentage | Concentrate / Water Ratio | Typical Use |
|---|---|---|
| 40% | 40 / 60 | Mild climates where freeze protection needs are lower |
| 50% | 50 / 50 | Common target for many vehicles |
| 60% | 60 / 40 | Colder conditions, if allowed by the coolant label |
| 70% | 70 / 30 | Often near the practical upper limit for many coolants |
Coolant Volume Unit Conversions
| Unit | Equivalent |
|---|---|
| 1 US gallon | 3.78541 liters, 4 quarts, or 128 US fluid ounces |
| 1 liter | 0.264172 US gallons or 1.05669 US quarts |
| 1 US quart | 0.946353 liters |
| 1 imperial gallon | 4.54609 liters |
Example Calculations
Example 1: Full refill at 50%
You have a 3 gallon cooling system and want a 50% antifreeze mix using concentrate and distilled water.
A = 3 * 50/100 = 1.5 gal
W = 3 - 1.5 = 1.5 gal
You need 1.5 gallons of antifreeze concentrate and 1.5 gallons of distilled water.
Example 2: Partial drain and refill with concentrate
Your system capacity is 3 gallons, the current mixture is 40% antifreeze, you drain 1 gallon, and you refill with concentrate.
A_final = 3*(40/100) - 1*(40/100) + 1*1
A_final = 1.8 gal
P_final = 1.8/3 * 100 = 60%
After the refill, the coolant mixture is 60% antifreeze.
FAQ
Can 50/50 premix make a different target percentage?
Not by itself during a full refill. A 50/50 premix is already 50% antifreeze and 50% water, so filling an empty system with only 50/50 premix gives about a 50% final mixture. To reach a different percentage, you need concentrate, water, or a calculated partial drain and refill.
What antifreeze percentage should you use?
Many vehicles commonly use a 50/50 mix, but the correct target depends on the coolant type, climate, and vehicle requirements. Do not assume that more antifreeze is always better. Very high antifreeze concentrations can reduce heat transfer and may fall outside the coolant manufacturer’s recommended range.
Why does the partial drain calculation assume the drained coolant has the same mix?
Once the engine has been run and the coolant has circulated, the antifreeze and water are treated as evenly mixed. The calculation assumes the portion drained has the same antifreeze percentage as the rest of the system. If the system was not mixed, the real final percentage may be different.
