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.
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
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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