Fuel Oil Mix Calculator
Find how much 2-stroke oil to add to your petrol (gas) for any ratio, in mL and fl oz, plus the petrol for the oil you have, how to fix a wrong mix and a quick chart for common cans.
Or type any ratio. Pick "% oil" to type it as a percentage (2% is 50:1).
How your fuel mix is worked out
A ratio of 50:1 means 50 parts petrol to 1 part oil, so oil = petrol ÷ 50.
- 1
Your petrol
5 L= 5,000 mL
- 2
Divide by the ratio
5,000 ÷ 50= 100 mL oil= 3.38 US fl oz
- 3
Add them up
5 + 0.1 L= 5.1 L
- 4
As a percentage
100 ÷ 50= 2% oil(1.96% of mix)
Read more: the formula, a worked example, a mix chart and tips
Two-stroke engines (in many chainsaws, trimmers, leaf blowers, small outboards, mopeds and dirt bikes) have no oil sump, so the oil travels in with the fuel. The ratio tells you how many parts of petrol (gas) get one part of 2-stroke oil. The calculator divides your petrol by that number, shows the oil in mL and fluid ounces, and can also work backwards or rescue a can you mixed wrong. To change other liquid units, use the volume converter.
Always follow the engine maker’s ratio. It is in the manual or printed on the machine or fuel cap. The oil bottle may suggest a ratio too, but the engine maker’s figure comes first. Too little oil can seize an engine; too much can foul the plug and smoke.
The formula
oil = petrol ÷ ratio
petrol = oil × ratio
total mix = petrol + oil
oil as % of petrol = 100 ÷ ratio · ratio = 100 ÷ oil %
oil as % of the mix = 100 ÷ (ratio + 1)
fix a mix made at A:1 to get B:1:
petrol in the can = mix × A ÷ (A + 1) (or the petrol you used) · oil in the can = petrol ÷ A
if B is bigger than A (too much oil): add petrol = oil × B − petrol
if B is smaller than A (too little oil): add oil = petrol ÷ B − oil
1 L = 1,000 mL · 1 US gal = 3.785411784 L = 128 US fl oz · 1 UK gal = 4.54609 L = 160 UK fl oz · 1 US fl oz = 29.5735 mL
Worked example
5 litres of petrol at 50:1. 5 L is 5 × 1,000 = 5,000 mL, so the oil is 5,000 ÷ 50 = 100 mL. In US fluid ounces that is 100 ÷ 29.5735 = 3.38 US fl oz (3.52 UK fl oz). The can then holds 5 + 0.1 = 5.1 L of mix. As a percentage the oil is 100 ÷ 50 = 2% of the petrol, or 100 ÷ 51 = 1.96% of the whole mix.
Fixing a mix: you put 5 L of petrol with oil for 25:1, but the engine wants 50:1. The can holds 5,000 ÷ 25 = 200 mL of oil. For 50:1 that oil needs 200 × 50 = 10,000 mL of petrol, so add 5 L of petrol to get 10.2 L of mix at 50:1. Going the other way, 5 L mixed at 100:1 has 50 mL of oil; 50:1 needs 5,000 ÷ 50 = 100 mL, so add 50 mL of oil.
Mix chart
| Ratio | 1 L | 5 L | 1 US gal | 1 UK gal | Oil % |
|---|---|---|---|---|---|
| 16:1 | 62.5 mL | 312.5 mL | 8 US fl oz | 284.1 mL | 6.25% |
| 20:1 | 50 mL | 250 mL | 6.4 US fl oz | 227.3 mL | 5% |
| 25:1 | 40 mL | 200 mL | 5.12 US fl oz | 181.8 mL | 4% |
| 32:1 | 31.3 mL | 156.3 mL | 4 US fl oz | 142.1 mL | 3.13% |
| 40:1 | 25 mL | 125 mL | 3.2 US fl oz | 113.7 mL | 2.5% |
| 50:1 | 20 mL | 100 mL | 2.56 US fl oz | 90.9 mL | 2% |
| 100:1 | 10 mL | 50 mL | 1.28 US fl oz | 45.5 mL | 1% |
US and UK gallons and fluid ounces are different sizes: a UK gallon is about 20% bigger than a US gallon. Unit sizes are exact legal definitions (checked 13 October 2026).
Mixing tips
- Use oil made for 2-stroke engines, not car (4-stroke) engine oil. For outboards, use oil made for water-cooled 2-strokes.
- Pour in about half the petrol, add all the oil, close the can and shake, then add the rest of the petrol and shake again.
- Mix only what you will use in a few weeks. Mixed fuel goes stale, especially petrol with ethanol in it.
- Label the can with the ratio and the date, so nobody pours 25:1 into a 50:1 machine by mistake.
- Engines with a separate oil tank (oil injection) do not need premix. Check before you add oil to the petrol.
Common questions
How much oil do I mix with 5 litres of petrol at 50:1?
100 mL. Divide the petrol by the ratio: 5,000 mL ÷ 50 = 100 mL of 2-stroke oil. That is about 3.38 US fl oz, and the can then holds 5.1 litres of mix.
How much oil for 1 gallon of gas at 50:1?
A US gallon is 128 US fl oz, so 128 ÷ 50 = 2.56 US fl oz (about 76 mL). At 40:1 it is 3.2 fl oz, at 32:1 it is 4 fl oz and at 25:1 it is 5.12 fl oz.
What does 50:1 mean?
50 parts petrol (gas) to 1 part oil. Every 50 litres of petrol gets 1 litre of oil, so every litre gets 20 mL. As a percentage the oil is 2% of the petrol.
Is 40:1 more oil than 50:1?
Yes. The smaller the first number, the richer the mix. 40:1 is 25 mL of oil per litre; 50:1 is 20 mL per litre. 25:1 is 40 mL per litre.
I mixed the wrong ratio. How do I fix it?
If there is too much oil, add petrol: oil already in × the ratio you want − petrol already in. If there is too little oil, add oil: petrol ÷ the ratio you want − oil already in. For example 5 L mixed at 25:1 has 200 mL of oil; to make it 50:1 add 5 L more petrol. Pick "Fix a mix" in Advanced.
What ratio should my engine use?
Always use the ratio in your engine maker’s manual or printed on the machine. Many modern hand-held tools use 50:1, older engines and some outboards use 25:1 to 32:1, and some oils say 100:1. Using too little oil can damage the engine.
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