40:1 Gas Oil Mix Calculator

A 40:1 gas-oil mix means 40 parts of gasoline to 1 part of 2-stroke oil. For example, 1 US gallon of gas requires exactly 3.2 fluid ounces of oil, or 1 liter of gas needs 25 milliliters of oil. This provides a balanced amount of lubrication that works well with semi-synthetic oils.

Use 40:1 for mid-generation 2-stroke engines from the 1990s-2000s, or when specifically required by your owner's manual. This ratio is ideal for equipment like Husqvarna and Echo chainsaws, most trimmers and leaf blowers, and small motorcycles with semi-synthetic oil. It offers a good balance between lubrication and clean burning.

For 5 liters of gasoline at a 40:1 ratio, you need 125 milliliters (mL) of 2-stroke oil.

For 1 US gallon of gasoline at a 40:1 ratio, you need exactly 3.2 fluid ounces (fl oz) of 2-stroke oil. This makes 40:1 a practical ratio for most small engine applications.

Each ratio serves different purposes. 40:1 is a middle ground: it has less smoke and carbon buildup than 32:1, but provides more lubrication than 50:1. Use 40:1 for mid-generation equipment, 32:1 for classic/high-RPM engines, and 50:1 for modern engines with full synthetic oil. Always follow manufacturer recommendations.

Use high-quality 2-stroke oil rated for your engine type. Semi-synthetic oils work excellently at 40:1 and provide better protection than mineral oils while being more affordable than full synthetics. Look for oils that meet JASO FD or ISO-L-EGD standards for best results.

Using 40:1 in a 50:1 engine will add 25% more oil than specified. While this provides extra lubrication, it may cause increased smoke and carbon deposits over time. It's generally safer to use a slightly richer mix (40:1 instead of 50:1) than too lean, but always follow manufacturer specifications when possible.

Using 40:1 in equipment designed for 32:1 provides 20% less oil. This may be insufficient for older engines that need the extra lubrication, especially under heavy loads or high RPM. Stick to the recommended 32:1 ratio for classic equipment unless the manufacturer approves a leaner mixture.

Yes, 40:1 produces noticeably less smoke than 32:1 because it contains about 20% less oil (3.2 oz vs 4 oz per gallon). This results in cleaner exhaust, less visible smoke, and reduced carbon buildup on spark plugs and exhaust ports while still providing adequate lubrication for most modern 2-stroke engines.

Premixed 40:1 fuel should be used within 30 days for best performance. Use fresh gasoline without ethanol if possible, and add a fuel stabilizer for storage up to 60-90 days. Always shake the container before use to ensure proper mixing. Store in approved containers in a cool, dry place away from direct sunlight and heat sources.