50:1 Fuel Mix — Gas to Oil Ratio Calculator & Chart
A 50:1 two-stroke fuel mix means 2.56 oz of 2-stroke oil for every US gallon of gas, or 20 ml of oil per litre. Use the calculator to get the exact amount for any quantity of fuel, then check the full 50:1 mix chart in gallons and litres below. It works the same for "2-cycle", "2-stroke" and "two-stroke" engines — it's all the same premix.
Advertisement
At 50:1 you add 2.56 oz of oil per gallon (20 ml per litre). For a 5-gallon can of gas that's 12.8 oz of 2-stroke oil.
Full mix chart
50:1 ratio
| Gallons of gas | oz of oil |
|---|---|
| 0.5 | 1.28 |
| 1 | 2.56 |
| 1.5 | 3.84 |
| 2 | 5.12 |
| 2.5 | 6.4 |
| 3 | 7.68 |
| 4 | 10.24 |
| 5 | 12.8 |
| 6 | 15.36 |
| Litres of gas | ml of oil |
|---|---|
| 1 | 20 |
| 2 | 40 |
| 3 | 60 |
| 4 | 80 |
| 5 | 100 |
| 10 | 200 |
| 15 | 300 |
| 20 | 400 |
| 25 | 500 |
What actually runs at 50:1
Fifty to one is the default for nearly every air-cooled handheld tool built in the last three decades. Stihl, Husqvarna, Echo, Shindaiwa, Makita and Ryobi all specify it across their current chainsaws, string trimmers, hedge trimmers, blowers and cut-off saws. Most modern carbureted two-stroke outboards run 50:1 as well, though with a marine TC-W3 oil rather than an air-cooled JASO oil.
If a tool was built after the mid-1990s and the tank decal has worn off, 50:1 is the most likely spec. The cap decal or the manual still decides it though: a relabelled older engine or a rebuild can call for something richer.
Why the standard moved to 50:1
The engines did not stop needing protection; the oils got better. JASO FC and FD grade oils, and full synthetics in particular, hold a lubricating film at a lower treat rate than the mineral oils the older 32:1 and 40:1 specs were written around.
Less oil in the charge also means less smoke, less carbon on the piston crown and exhaust port, and fewer fouled plugs. That is why emissions-era engines moved in this direction instead of staying rich.
Measuring 50:1 without a calculator
The single-use bottles on the shelf are sized around this ratio: a 2.6 oz bottle treats 1.02 US gallon at 50:1, and a 16 oz pint covers 6.25 gallons. In metric it is 20 ml per litre, so a 100 ml bottle treats 5 litres and a 1-litre jug of oil makes 50 litres of mix.
A 2-gallon can takes 5.12 oz of oil and a 5-gallon can takes 12.8 oz. Measure into the empty can, add the gas second, and shake the sealed can before you fill the tank.
Common 50:1 mistakes and what they look like
- Emptying one 2.6 oz bottle into a 2-gallon can. That halves the oil (roughly 100:1) and is the single most common cause of a scored piston in handheld equipment.
- Mixing in the machine's tank instead of the can. The oil never disperses properly, so the engine runs the first part of that tank close to straight gas.
- Running a 40:1 mix out of habit in a 50:1 machine. It rarely hurts the engine, but it smokes more and loads the spark-arrestor screen faster.
Too little oil shows up as gradual power loss, a scored piston skirt and eventually a seizure. Too much shows up as blue smoke at idle, a wet black spark plug and a clogged arrestor screen.
Common questions
[01] What is 50:1 in ounces per gallon?
50:1 is 2.56 fluid ounces of oil per US gallon of gas (128 ÷ 50 = 2.56).
[02] What is 50:1 in ml per litre?
50:1 is 20 ml of oil per litre of gas (1000 ÷ 50 = 20).
[03] What happens if I add too much oil at 50:1?
Too much oil makes the engine run rich — it can smoke, foul the spark plug and lose power. A little extra is safer than too little, but stay close to 50:1 and follow your owner's manual.
[04] Can I run 50:1 in an engine that specifies 40:1?
Only if the equipment or oil manufacturer allows it. A 50:1 mix carries 20 percent less oil than 40:1, so the engine gets less lubrication than it was designed for. When in doubt, mix the richer of the two ratios.
[05] Is 50:1 the same for an outboard as for a chainsaw?
The arithmetic is the same (2.56 oz per gallon), but the oil is not. A water-cooled outboard needs a marine TC-W3 oil and an air-cooled chainsaw needs a JASO-rated oil. Do not swap them.