100:1 Fuel Mix — Gas to Oil Ratio Calculator & Chart
A 100:1 two-stroke fuel mix means 1.28 oz of 2-stroke oil for every US gallon of gas, or 10 ml of oil per litre. Use the calculator to get the exact amount for any quantity of fuel, then check the full 100:1 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.
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At 100:1 you add 1.28 oz of oil per gallon (10 ml per litre). For a 5-gallon can of gas that's 6.4 oz of 2-stroke oil.
Full mix chart
100:1 ratio
| Gallons of gas | oz of oil |
|---|---|
| 0.5 | 0.64 |
| 1 | 1.28 |
| 1.5 | 1.92 |
| 2 | 2.56 |
| 2.5 | 3.2 |
| 3 | 3.84 |
| 4 | 5.12 |
| 5 | 6.4 |
| 6 | 7.68 |
| Litres of gas | ml of oil |
|---|---|
| 1 | 10 |
| 2 | 20 |
| 3 | 30 |
| 4 | 40 |
| 5 | 50 |
| 10 | 100 |
| 15 | 150 |
| 20 | 200 |
| 25 | 250 |
100:1 is not a default ratio
No mainstream equipment maker puts 100:1 on the tank decal today. The ratio turns up in two specific situations: when the oil is explicitly rated for it (AMSOIL Saber Professional is the best-known example), and on some older machines that were sold alongside the maker's own 100:1 oil, such as certain Homelite and Tanaka equipment.
Outside those two cases, 100:1 simply means half the oil the engine expects. An ordinary 50:1 oil does not change its properties because you dilute it further.
Why the margin for error is so small
At 100:1 the dose is only 1.28 oz per gallon (10 ml per litre). Being half an ounce out on a one-gallon can is a far bigger proportional error than the same half ounce at 32:1, where the dose is four times larger.
That is why this ratio deserves a syringe or a fine graduated cup rather than a splash from the bottle. A 5-gallon can takes 6.4 oz, and a 16 oz pint of oil stretches to 12.5 gallons of mix.
Warranty and common sense
Most manufacturers tie the warranty to the ratio in the manual. Even with an oil rated for 100:1, a chainsaw whose decal says 50:1 is out of spec when you mix it twice as lean, and that can matter in a claim.
100:1 makes sense when the oil maker certifies it and the equipment maker does not require otherwise. It never makes sense as a way to stretch a bottle of oil.
Common questions
[01] What is 100:1 in ounces per gallon?
100:1 is 1.28 fluid ounces of oil per US gallon of gas (128 ÷ 100 = 1.28).
[02] What is 100:1 in ml per litre?
100:1 is 10 ml of oil per litre of gas (1000 ÷ 100 = 10).
[03] What happens if I add too much oil at 100:1?
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 100:1 and follow your owner's manual.
[04] Is 100:1 safe in any two-stroke engine?
No. 100:1 is only safe with an oil explicitly rated for that ratio, in an engine whose maker does not require otherwise. With an ordinary 50:1 oil you would be supplying half the oil the engine expects.
[05] Which oils are rated for 100:1?
The ones that say so on the bottle. AMSOIL Saber Professional is the best-known oil formulated to run as lean as 100:1. Always check the label before mixing that lean.