Calculate the exact amount of oil needed for your gasoline.
US Gallons (Result in fl oz)
Liters (Result in ml)
Imperial Gallons (Result in fl oz)
32:140:150:1100:1
Enter the first number of the ratio (e.g., enter "50" for a 50:1 mix).
Add this amount of 2-stroke oil
0 oz
Ratio: 50:1
Understanding 2-Stroke Oil Mixtures
Correctly mixing oil and fuel is crucial for the longevity and performance of any 2-stroke engine. Unlike 4-stroke engines which have a dedicated oil reservoir for lubrication, 2-stroke engines rely on oil mixed directly into the gasoline to lubricate the piston, cylinder walls, and crank bearings. Failing to get this ratio right can lead to seized engines (too little oil) or fouled spark plugs and excessive smoke (too much oil).
Warning: Always check your equipment's user manual for the manufacturer's recommended ratio. Using a generic ratio like 50:1 on an older machine designed for 32:1 can cause catastrophic engine failure.
Common Premix Ratios Explained
Different engines require different concentrations of oil. Here are the most standard ratios found in chainsaws, dirt bikes, weed eaters, and outboard motors:
50:1 (2%): The modern standard for most high-quality handheld equipment (Stihl, Husqvarna) and many modern outboards. It is a leaner mix that produces less smoke.
40:1 (2.5%): A very common ratio for older chainsaws and many 2-stroke dirt bikes (like 125cc or 250cc motocross bikes) to provide extra protection at high RPMs.
32:1 (3.125%): Used in older equipment (pre-1990s) or high-performance racing engines that require heavy lubrication. This is a "rich" mixture.
100:1 (1%): Specialized ratio primarily used by certain outboard motors (like older Yamaha or Evinrude models) and some synthetic oils like Amsoil Saber (though check warranty requirements first).
How the Math Works
The calculation changes depending on your unit of measurement. Our calculator handles this automatically, but here is the logic for manual calculation:
US Gallons to Fluid Ounces
There are 128 fluid ounces in 1 US Gallon.
Formula: (Gallons of Gas × 128) ÷ Ratio Number = Ounces of Oil
Example for 50:1 with 1 gallon: (1 × 128) / 50 = 2.56 oz of oil.
Liters to Milliliters
There are 1000 milliliters in 1 Liter.
Formula: (Liters of Gas × 1000) ÷ Ratio Number = Milliliters of Oil
Example for 40:1 with 5 liters: (5 × 1000) / 40 = 125 ml of oil.
Quick Reference Chart (US Gallons)
Fuel Amount
50:1 Ratio
40:1 Ratio
32:1 Ratio
1 Gallon
2.6 oz
3.2 oz
4.0 oz
2 Gallons
5.1 oz
6.4 oz
8.0 oz
5 Gallons
12.8 oz
16.0 oz
20.0 oz
Tips for Mixing
Add Oil First: Pour the required amount of 2-stroke oil into your gas can before adding the fuel. The force of the fuel coming from the pump helps mix the oil.
Use Fresh Fuel: Ethanol-blended fuels degrade quickly. Try to use non-ethanol gas for small engines, or use a fuel stabilizer if the mix will sit for more than 30 days.
Shake It: Even if mixed previously, always shake your gas can before filling your equipment, as oil can sometimes separate or settle over time.
Label Your Cans: Never store mixed gas in an unmarked can. accidentally putting pure gas in a 2-stroke engine will destroy it in minutes, and putting mixed gas in a 4-stroke car can damage sensors.
function setRatio(val) {
document.getElementById('oilRatio').value = val;
}
function updateLabels() {
var unit = document.getElementById('unitType').value;
// Clear result when unit changes to avoid confusion
document.getElementById('resultBox').style.display = 'none';
}
function calculateMix() {
var fuelInput = document.getElementById('fuelAmount').value;
var ratioInput = document.getElementById('oilRatio').value;
var unit = document.getElementById('unitType').value;
// Validation
if (fuelInput === "" || isNaN(fuelInput) || fuelInput <= 0) {
alert("Please enter a valid amount of fuel.");
return;
}
if (ratioInput === "" || isNaN(ratioInput) || ratioInput <= 0) {
alert("Please enter a valid ratio (e.g., 50).");
return;
}
var fuel = parseFloat(fuelInput);
var ratio = parseFloat(ratioInput);
var result = 0;
var resultUnit = "";
var fuelUnitLabel = "";
if (unit === "gallons") {
// US Gallons to US Ounces
// 1 US Gallon = 128 US fl oz
result = (fuel * 128) / ratio;
resultUnit = "fl oz";
fuelUnitLabel = "Gallons";
} else if (unit === "liters") {
// Liters to Milliliters
// 1 Liter = 1000 ml
result = (fuel * 1000) / ratio;
resultUnit = "ml";
fuelUnitLabel = "Liters";
} else if (unit === "imperial") {
// Imperial Gallons to Imperial Ounces
// 1 Imperial Gallon = 160 Imperial fl oz
result = (fuel * 160) / ratio;
resultUnit = "fl oz (Imp)";
fuelUnitLabel = "Imp Gallons";
}
// Formatting output
// If result is small (less than 10), show 2 decimals. If large, show 1.
var formattedResult = result < 10 ? result.toFixed(2) : result.toFixed(1);
var resultBox = document.getElementById('resultBox');
var resultValue = document.getElementById('resultValue');
var ratioDisplay = document.getElementById('ratioDisplay');
var totalMix = document.getElementById('totalMix');
resultValue.innerHTML = formattedResult + " " + resultUnit + "";
ratioDisplay.innerText = "Target Ratio: " + ratio + ":1";
// Total volume context
totalMix.innerText = "To create " + fuel + " " + fuelUnitLabel + " of mix.";
resultBox.style.display = "block";
}