*Add this amount of oil to your gasoline container.
Understanding 2-Stroke Fuel Ratios
Operating a 2-stroke engine requires a precise mixture of gasoline and specialized 2-stroke oil. Unlike 4-stroke engines which have a separate oil reservoir for lubrication, 2-stroke engines rely on the fuel itself to lubricate the internal components (piston, rings, and bearings). Using the Oil to Gas Ratio Calculator above ensures you mix your fuel correctly, preventing engine seizures from too little oil or fouled spark plugs from too much oil.
Common Oil Mixture Ratios
Different manufacturers specify different ratios based on the engine's tolerance and the quality of oil used. Always consult your owner's manual.
Ratio
Common Applications
Oil per Gallon (US)
50:1
Modern chainsaws, weed eaters, leaf blowers (Stihl, Husqvarna, Echo).
2.6 oz
40:1
Older yard equipment, some generic 2-stroke engines.
3.2 oz
32:1
Dirt bikes, ATVs, and high-performance racing engines.
4.0 oz
25:1
Engine break-in periods or vintage outboards.
5.1 oz
How to Mix 2-Stroke Fuel Correctly
Proper mixing technique is just as important as the ratio. Follow these steps for a safe premix:
Use a Clean Container: Never mix fuel directly in the equipment's tank. Use a dedicated gas can.
Add Gas First: Pour about half of your gasoline into the container.
Add Oil: Pour the calculated amount of 2-stroke oil into the container.
Agitate: Close the container and shake it gently to mix the oil and gas.
Top Off: Add the remaining gasoline and shake gently one more time.
Why Math Matters: Lean vs. Rich
The "Ratio" refers to parts of gasoline to parts of oil. A 50:1 ratio means 50 parts gasoline to 1 part oil.
Running Lean (Higher Ratio, e.g., 100:1): Using less oil than recommended reduces lubrication, causing friction, overheating, and potentially catastrophic engine failure (piston seizure).
Running Rich (Lower Ratio, e.g., 20:1): Using more oil than recommended causes excessive smoke, carbon buildup in the exhaust port, and fouled spark plugs, making the engine hard to start.
US vs. Metric Measurements
Our calculator handles both systems. In the US, the standard calculation is based on 128 fluid ounces in a gallon. For metric users, the calculation is based on 1000 milliliters in a liter.
Formula (US): (Gallons of Gas × 128) ÷ Ratio = Ounces of Oil
Formula (Metric): (Liters of Gas × 1000) ÷ Ratio = Milliliters of Oil
For example, if you need a 50:1 mix for 1 gallon of gas: (1 × 128) / 50 = 2.56 fluid ounces of oil.
var currentUnit = 'us';
function toggleUnits(unit) {
currentUnit = unit;
var gasLabel = document.getElementById('gasLabel');
var gasInput = document.getElementById('gasAmount');
if (unit === 'us') {
gasLabel.innerText = "Fuel Amount (Gallons)";
gasInput.placeholder = "e.g. 1";
} else {
gasLabel.innerText = "Fuel Amount (Liters)";
gasInput.placeholder = "e.g. 5";
}
// Hide result when switching units to avoid confusion until recalculated
document.getElementById('resultBox').style.display = 'none';
}
function checkCustomRatio() {
var select = document.getElementById('ratioSelect');
var customGroup = document.getElementById('customRatioGroup');
if (select.value === 'custom') {
customGroup.style.display = 'block';
} else {
customGroup.style.display = 'none';
}
}
function calculateOilMix() {
// Get inputs
var gasAmount = parseFloat(document.getElementById('gasAmount').value);
var ratioSelect = document.getElementById('ratioSelect').value;
var customRatio = parseFloat(document.getElementById('customRatioInput').value);
// Determine ratio value
var ratio = 0;
if (ratioSelect === 'custom') {
ratio = customRatio;
} else {
ratio = parseFloat(ratioSelect);
}
// Validation
if (isNaN(gasAmount) || gasAmount <= 0) {
alert("Please enter a valid amount of gasoline.");
return;
}
if (isNaN(ratio) || ratio <= 0) {
alert("Please select or enter a valid ratio.");
return;
}
var oilNeeded = 0;
var totalMix = 0;
var unitLabel = "";
var totalUnitLabel = "";
// Calculation Logic
if (currentUnit === 'us') {
// 1 Gallon = 128 fl oz
// Formula: (Gallons * 128) / Ratio = Oil in oz
oilNeeded = (gasAmount * 128) / ratio;
unitLabel = "fl oz";
totalUnitLabel = "Gallons";
// Total volume isn't usually sum in gallons because oil is small,
// but physically it is Gas + (Oil/128).
// However, usually people say "1 gallon of mix" meaning 1 gal gas + oil.
// We will display just the input gas as the base.
} else {
// 1 Liter = 1000 ml
// Formula: (Liters * 1000) / Ratio = Oil in ml
oilNeeded = (gasAmount * 1000) / ratio;
unitLabel = "ml";
totalUnitLabel = "Liters";
}
// Rounding
// For US ounces, 2 decimal places is good (precision).
// For Metric ml, integer is usually fine, but 1 decimal is safer.
var displayOil = (currentUnit === 'us') ? oilNeeded.toFixed(2) : oilNeeded.toFixed(1);
// Update DOM
var resultBox = document.getElementById('resultBox');
var oilResult = document.getElementById('oilResult');
var totalResult = document.getElementById('totalResult');
oilResult.innerText = displayOil + " " + unitLabel;
totalResult.innerText = "For " + gasAmount + " " + totalUnitLabel + " of Gas @ " + ratio + ":1 Ratio";
resultBox.style.display = 'block';
}