Two-stroke engines are common in garden equipment like chainsaws, leaf blowers, and strimmers, as well as in some older motorcycles and scooters. Unlike four-stroke engines, they don't have a separate oil sump for lubrication. Instead, a special 2-stroke oil must be precisely mixed with the petrol to lubricate critical engine components like the piston, cylinder, and crankshaft bearings during operation.
Using the correct fuel-to-oil ratio is vital for engine health. Too little oil can lead to overheating, excessive wear, and catastrophic engine seizure. Too much oil can cause fouled spark plugs, excessive smoke, and carbon buildup on internal components, leading to poor performance. This calculator helps you determine the exact amount of oil to add for any quantity of petrol.
Understanding Mix Ratios
The mix ratio is expressed as parts of petrol to one part of oil (e.g., 50:1). This means you need 50 parts of petrol for every 1 part of oil.
50:1 Ratio: A common ratio for modern, high-quality equipment. It means for every 50 litres of petrol, you add 1 litre of oil.
40:1 Ratio: Often recommended for slightly older or more demanding equipment.
25:1 Ratio: A richer oil mix typically used for older, vintage engines or during the break-in period for some new engines.
Crucially, always consult your equipment's user manual for the manufacturer's recommended mix ratio. Using the wrong ratio can void your warranty and damage your engine.
2-Stroke Petrol Mix Calculator
Example Calculation
Let's say you have a 5-litre can of petrol and your chainsaw requires a 40:1 mix ratio.
Enter Petrol Amount: 5
Enter Mix Ratio: 40
Calculation: The calculator divides the petrol amount by the ratio (5 Litres / 40 = 0.125 Litres of oil).
Result: It then converts this to a more practical unit, millilitres (0.125 Litres * 1000 = 125 ml).
You would need to add exactly 125 ml of 2-stroke oil to your 5 litres of petrol.
Best Practices for Mixing
Use a Clean Container: Always mix your fuel in a separate, clean, and approved fuel container, not directly in the equipment's tank.
Mixing Order: For the best mixture, pour in about half of the petrol first, then add the full amount of 2-stroke oil. Seal the container and shake it vigorously for 15-20 seconds. Then, add the remaining petrol and shake again.
Use Quality Oil: Always use a high-quality 2-stroke oil that meets JASO FD or ISO-L-EGD specifications.
Don't Store for Too Long: Mixed fuel can degrade over time. Try to only mix what you expect to use within a month for optimal engine performance and longevity.
function calculateMix() {
var petrolAmountStr = document.getElementById("petrolAmount").value;
var mixRatioStr = document.getElementById("mixRatio").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "";
if (petrolAmountStr === "" || mixRatioStr === "") {
resultDiv.innerHTML = "Please fill in both fields.";
return;
}
var petrolAmount = parseFloat(petrolAmountStr);
var mixRatio = parseFloat(mixRatioStr);
if (isNaN(petrolAmount) || isNaN(mixRatio) || petrolAmount <= 0 || mixRatio <= 0) {
resultDiv.innerHTML = "Please enter valid, positive numbers for both petrol amount and mix ratio.";
return;
}
var oilAmountLitres = petrolAmount / mixRatio;
var oilAmountMl = oilAmountLitres * 1000;
var totalVolume = petrolAmount + oilAmountLitres;
var resultHTML = "
Calculation Result:
" +
"For " + petrolAmount.toFixed(2) + " Litres of petrol at a " + mixRatio + ":1 ratio, you need to add:" +
"
" +
"" + oilAmountMl.toFixed(2) + " ml of 2-stroke oil." +
"
" +
"This will give you a total fuel volume of approximately " + totalVolume.toFixed(3) + " Litres.";
resultDiv.innerHTML = resultHTML;
}