How to Mix 2-Stroke Fuel: The Complete Guide

Mixing 2-stroke fuel (also called 2-cycle or two-stroke premix) means adding a measured amount of oil to gasoline so the engine is lubricated as it burns its fuel. A two-stroke has no oil sump; the only oil the crankshaft bearings, connecting rod and piston ever see is the oil you put in the can. Get the ratio right and a chainsaw, trimmer, blower or dirt bike runs clean for years. Get it wrong in one direction and you foul plugs; get it wrong in the other and you score a piston. Here is the whole routine, with the numbers.

The one rule: oil = gas ÷ ratio

Every 2-stroke ratio is written as gas:oil, so 50:1 means 50 parts gas to 1 part oil. A US gallon is 128 fluid ounces and a litre is 1,000 millilitres, which gives two formulas worth memorising:

• Ounces of oil per gallon = 128 ÷ ratio. At 50:1 that is 2.56 oz.
• Millilitres of oil per litre = 1000 ÷ ratio. At 50:1 that is 20 ml.

For the ratios you will actually meet:

Ratio	Per US gallon	Per 2.5 gallons	Per litre	Per 5 litres
50:1	2.56 oz	6.4 oz	20 ml	100 ml
40:1	3.2 oz	8 oz	25 ml	125 ml
32:1	4 oz	10 oz	31.25 ml	156.25 ml
25:1	5.12 oz	12.8 oz	40 ml	200 ml

For any other amount, use the calculator. It switches between gallons and litres and works backwards too, if you know how much oil you have and want to know how much gas it treats:

Fuel → oil / Oil → fuel

Fuel → oil Oil → fuel

Amount of fuel

Gallons (US) Litres

Equipment (optional) Choose equipment… Chainsaw (50:1) String trimmer / weed eater (50:1) Leaf blower (50:1) 2-stroke lawn mower (50:1) Dirt bike / motorcycle (40:1) Outboard motor (50:1)

Mix ratio

100:1 50:1 40:1 32:1 25:1 20:1

Custom ratio (X : 1)

Calculate Reset Copy link to this mix

Add this much oil

12.8 oz

≈ 378.54 ml

Add 12.8 oz of 2-stroke oil to 5 gal of gas at a 50:1 ratio.

Step 1: find your ratio

Look in this order: the decal on the fuel cap or tank, the owner’s manual, then the maker’s website for your model number. Most modern handheld equipment from Stihl, Husqvarna and Echo is 50:1, which is why the calculator defaults to it. Older equipment, budget tools, dirt bikes and outboards are where the ratio varies, and the chainsaw, string trimmer, dirt bike and outboard pages cover the common exceptions for each.

If the tool has no decal and no paperwork, mix at 40:1. A slightly rich mix costs some smoke and a dirtier spark arrestor screen; a lean guess can cost the engine.

Step 2: pick the gas

Use fresh pump gas at the octane your manual asks for, which on most handheld equipment is 89 or higher. Keep ethanol at 10 percent or less: E10 is fine, E15 is not approved for small off-road engines and will attack fuel lines and carburettor diaphragms. Ethanol-free gas is better still if a station near you sells it, because ethanol absorbs water and is the main reason mixed fuel goes stale. Buy gas for mixing in the amount you will use in a month, not a season.

Step 3: pick the oil

Use an oil made for two-stroke engines, never automotive motor oil, and match its rating to the engine. Air-cooled equipment (saws, trimmers, blowers, dirt bikes) wants JASO FD or ISO-L-EGD. Water-cooled outboards want NMMA TC-W3. The two are not interchangeable, and TC-W3 vs JASO FD explains why. If you are choosing between brands, the best 2-stroke oil guide ranks them by use.

Step 4: measure, then mix in the right order

1. Start with a clean, empty, approved fuel can, labelled with the ratio. A can that last held straight gas for the mower is how a lot of engines get run without oil.
2. Measure the oil for the amount of gas you are about to add, using a ratio cup, a marked bottle or a syringe for small batches. The measuring tools guide covers what works.
3. Pour the oil into the empty can first. Oil added on top of a full can floats in a layer and takes far more shaking to blend.
4. Add about half the gas, cap the can and shake it for ten seconds.
5. Add the rest of the gas and shake again. The incoming fuel does most of the stirring for you.
6. Write the date on the can, then fill the equipment’s tank from it.

One point catches people often enough to repeat: the 2.6 oz single-use bottles sold by Echo, Stihl and Husqvarna are sized for one gallon at 50:1. Empty one into a half-full can and you have mixed 25:1; empty one into a 2.5 gallon can and you have mixed roughly 123:1.

Step 5: keep the batch fresh

Mixed fuel does not last as long as people assume. With ordinary ethanol-blended gas, plan on about a month. A stabiliser, added when you mix rather than when the fuel is already old, stretches that to several months. Store the can sealed, out of the sun and off a concrete floor where temperature swings pull moist air in through the vent.

Before any tool sits for the season, either run the tank dry or fill it with stabilised or ethanol-free fuel, and pour stale mix into your car’s tank a little at a time rather than into the engine. The full fall routine, machine by machine, is in how to winterize 2-stroke engines, and the checklist for bringing equipment back after winter is in spring startup for 2-stroke lawn equipment.

Signs the mix is wrong

Too much oil shows up quickly and is cheap to fix: heavy blue smoke that does not clear once warm, a wet black plug, oil dripping from the muffler, and a spark arrestor screen that clogs within a few tanks.

Too little oil is quiet until it is expensive. An engine running lean often feels strong and revs freely, then loses power when hot, and finally seizes. If you suspect a batch was mixed lean, stop using it rather than finishing the can.

Where to go next

For printable reference tables, see the 50:1, 40:1 and 32:1 pages, the mix charts, or the 2-stroke mix chart, which puts every ratio in gallons and litres on one page. For specific machines, the Echo weed eater ratio guide and the leaf blower gas oil mix guide cover the two tools most people own, and the outboard fuel mix guide covers ratios for boat motors by brand and model year.