Two Stroke Ratio Calculator

Two-Stroke Fuel Ratio Calculator

Easily determine the correct amount of oil to mix with your gasoline for any two-stroke engine.

function calculateTwoStrokeRatio() { var gasAmount = parseFloat(document.getElementById('gasAmount').value); var mixRatio = parseFloat(document.getElementById('mixRatio').value); var gasUnit = document.getElementById('gasUnit').value; var resultDiv = document.getElementById('result'); if (isNaN(gasAmount) || isNaN(mixRatio) || gasAmount <= 0 || mixRatio <= 0) { resultDiv.innerHTML = 'Please enter valid positive numbers.'; return; } var oilInOunces; var oilInMilliliters; // Conversion factors var ouncesPerGallon = 128; var mlPerLiter = 1000; var litersPerGallon = 3.78541; var gallonsPerLiter = 0.264172; if (gasUnit === 'gallons') { // Calculate oil needed in ounces and ml when gas is in gallons oilInOunces = (gasAmount / mixRatio) * ouncesPerGallon; var gasInLiters = gasAmount * litersPerGallon; oilInMilliliters = (gasInLiters / mixRatio) * mlPerLiter; } else { // gasUnit is 'liters' // Calculate oil needed in ml and ounces when gas is in liters oilInMilliliters = (gasAmount / mixRatio) * mlPerLiter; var gasInGallons = gasAmount * gallonsPerLiter; oilInOunces = (gasInGallons / mixRatio) * ouncesPerGallon; } resultDiv.innerHTML = 'Add: ' + oilInOunces.toFixed(2) + ' fl oz' + ' or ' + '' + oilInMilliliters.toFixed(2) + ' ml of oil.'; }

Understanding Two-Stroke Fuel Mixtures

Two-stroke engines, commonly found in chainsaws, leaf blowers, string trimmers, dirt bikes, and some marine outboards, require a special fuel mixture. Unlike four-stroke engines that have a separate oil system, two-stroke engines lubricate their internal components (like the piston and crankshaft) with oil that is pre-mixed directly with the gasoline. Getting this fuel-to-oil ratio correct is critical for the engine's health, performance, and longevity.

Why the Correct Ratio is Crucial

Using an incorrect fuel-to-oil ratio can lead to serious engine problems:

• Too Little Oil: This is the most dangerous scenario. Insufficient oil leads to inadequate lubrication, causing increased friction and heat. This can quickly result in piston scuffing, bearing failure, and catastrophic engine seizure. The engine is effectively starved of its lifeblood.
• Too Much Oil: While less immediately destructive, an oil-rich mixture can cause its own set of problems. These include fouled spark plugs, excessive smoke, heavy carbon buildup on the piston and exhaust port, and reduced engine performance. Over time, this buildup can restrict exhaust flow and lead to overheating.

Always consult your equipment's owner's manual for the manufacturer's recommended ratio. Using our calculator ensures you mix that ratio accurately every time.

How to Read a Two-Stroke Ratio

A ratio like 50:1 (read as "fifty to one") means you need to mix 50 parts of gasoline with 1 part of oil. The first number always represents the gasoline, and the second number (always 1) represents the oil.

Here is a quick reference for common ratios and the amount of oil needed per one US gallon of gasoline:

• 25:1 Ratio: 5.12 fl oz of oil per gallon of gas
• 32:1 Ratio: 4.00 fl oz of oil per gallon of gas
• 40:1 Ratio: 3.20 fl oz of oil per gallon of gas
• 50:1 Ratio: 2.56 fl oz of oil per gallon of gas

Practical Example: Mixing Fuel for a Chainsaw

Let's say you have a chainsaw that requires a 40:1 fuel ratio, and you want to mix 2 gallons of fuel.

1. Enter 2 into the "Gasoline Amount" field and ensure "Gallons" is selected.
2. Enter 40 into the "Fuel/Oil Ratio" field.
3. Click "Calculate Oil Needed".

The calculator will show that you need to add 6.40 fl oz (or 189.27 ml) of two-stroke oil to your 2 gallons of gasoline to achieve the correct 40:1 mixture. This simple tool removes guesswork and helps protect your valuable equipment.