Two Stroke Mixture Calculator

Two-Stroke Fuel Mixture Calculator

Calculate the exact amount of oil needed for your gas mix.

Required Oil:

function calculateTwoStrokeMix() { var fuel = parseFloat(document.getElementById('fuelQuantity').value); var unit = document.getElementById('fuelUnit').value; var ratio = parseFloat(document.getElementById('ratioPart').value); var resultDiv = document.getElementById('result-display'); var oilDisplay = document.getElementById('oilVolume'); var summary = document.getElementById('mixSummary'); if (isNaN(fuel) || isNaN(ratio) || fuel <= 0 || ratio <= 0) { alert('Please enter valid positive numbers for fuel amount and ratio.'); return; } var oilRequired = 0; var unitLabel = ""; if (unit === "liters") { // Conversion: (Liters / Ratio) * 1000 to get milliliters oilRequired = (fuel / ratio) * 1000; unitLabel = "ml (milliliters)"; } else if (unit === "gallons") { // US Gallon Conversion: (Gallons / Ratio) * 128 to get fluid ounces oilRequired = (fuel / ratio) * 128; unitLabel = "fl oz (US Fluid Ounces)"; } else if (unit === "ukgallons") { // UK Gallon Conversion: (Gallons / Ratio) * 160 to get fluid ounces oilRequired = (fuel / ratio) * 160; unitLabel = "fl oz (UK Fluid Ounces)"; } oilDisplay.innerHTML = oilRequired.toFixed(2) + " " + unitLabel; summary.innerHTML = "Mix " + oilRequired.toFixed(2) + " " + unitLabel + " of oil into " + fuel + " " + unit + " of gasoline for a " + ratio + ":1 ratio."; resultDiv.style.display = "block"; }

Mastering the Two-Stroke Fuel Mix

A two-stroke engine (often found in chainsaws, weed eaters, outboard motors, and dirt bikes) lacks a dedicated oiling system. Unlike a car engine where oil stays in the crankcase, a two-stroke engine requires lubrication to be mixed directly into the fuel. Using the wrong mixture ratio is one of the leading causes of engine failure.

Why the Ratio Matters

The "Ratio" represents parts of gasoline to parts of oil. For example, a 50:1 ratio means for every 50 units of gasoline, you add 1 unit of two-stroke oil.

• Too Little Oil (Lean): Results in excessive friction, overheating, and can lead to "seizing" the engine where the piston welds itself to the cylinder wall.
• Too Much Oil (Rich): Causes "smoke," fouled spark plugs, carbon buildup in the exhaust port, and sluggish engine performance.

Common Two-Stroke Ratios Reference Table

Ratio	Oil per 5 Liters (ml)	Oil per 1 US Gallon (oz)
25:1	200 ml	5.12 fl oz
32:1	156 ml	4.0 fl oz
40:1	125 ml	3.2 fl oz
50:1	100 ml	2.56 fl oz

Step-by-Step: How to Mix Two-Stroke Fuel

1. Identify the Ratio: Check your equipment's manual or the fuel cap. Most modern equipment uses 40:1 or 50:1.
2. Use Fresh Gas: Always use fresh, high-octane gasoline (89 or higher is often recommended). Avoid ethanol if possible, as it attracts moisture.
3. Add Oil First: If possible, pour the calculated amount of two-stroke oil into an empty, clean fuel canister first.
4. Add Gasoline: Fill the canister with the measured amount of gas. Adding gas after oil helps the mixture blend.
5. Shake Well: Tighten the cap and shake the canister vigorously to ensure the oil and gas are fully homogenized.

Pro Tip: Never mix fuel directly in the equipment's fuel tank. Always use a separate mixing container to ensure the ratio is precise and the liquids are properly combined.

Frequently Asked Questions

Can I use car motor oil for my 2-stroke mix?
No. Two-stroke oil is specifically designed to burn cleanly and mix with gasoline. Standard motor oil will cause heavy carbon deposits and may foul your engine.

How long does mixed fuel stay fresh?
Mixed fuel begins to degrade after 30 days. If you aren't using the fuel within a month, add a fuel stabilizer or mix smaller batches.

What if I don't know the ratio for my old engine?
Older engines (pre-1970s) often used 16:1 or 20:1. Most equipment from the 80s and 90s uses 32:1 or 40:1. When in doubt, a slightly "oiler" mix like 32:1 is safer than a lean 50:1, though it may cause more smoke.