Windshield Washer Fluid Mix Calculator
Calculate the correct washer fluid concentrate-to-water ratio for your tank size and freeze protection level.
Works for temperatures down to -40 degrees.
Washer Fluid Mix
How Windshield Washer Fluid Is Calculated
Windshield washer fluid is a mix of water and methanol (or ethanol) concentrate. The dilution ratio determines the freeze protection level.
Freeze Point Formula: The freeze point depends on the methanol concentration by volume. Most concentrates are 50–100% methanol-based.
Common Dilution Ratios and Freeze Protection:
| Mix Ratio (Concentrate:Water) | Freeze Protection |
|---|---|
| 1:3 (25% concentrate) | −5°C (23°F) |
| 1:1 (50% concentrate) | −20°C (−4°F) |
| 3:1 (75% concentrate) | −37°C (−35°F) |
| Undiluted (100%) | −45°C (−49°F) |
Tank Capacity Reference:
- Most passenger cars: 2.5–3.5 liters
- SUVs and trucks: 3.5–5.0 liters
- Calculate your needed mix:
Concentrate Needed = Tank Size × Concentrate Fraction
Worked Example: You have a 3-liter tank and live in an area that gets to −20°C. You need a 1:1 mix:
- Concentrate needed = 3.0 × 0.5 = 1.5 liters concentrate
- Water needed = 1.5 liters water
Practical Tips:
- Never use plain water — it freezes in the reservoir, lines, and nozzles and can crack the pump
- Summer formula: typically 30% concentrate + bug remover additives
- Winter formula: 50–100% depending on your minimum temperature
- Pre-mixed bottles are convenient but cost 2–3× more than concentrate
- Methanol-based fluid can damage paint if overspray is heavy — rinse promptly