Stihl Chainsaw Gas Mix: Fuel Ratio for Every MS Model
Published November 2, 2026 · 8 min read
The Stihl chainsaw fuel ratio is 50:1: 2.56 oz of 2-stroke oil per US gallon of gas, or 20 ml per litre, which is 100 ml in a 5 litre can. It does not change with the size of the saw. Stihl sets the ratio for the whole brand, and its US mixing guide puts it in one line: all Stihl gasoline-powered equipment uses a 50:1 gas and oil mixture. The MS 172 a homeowner keeps for storm cleanup and the MS 500i a logger runs all day burn the same mix from the same can. What does change between them is how much gas they go through, which oil and gas you put in, and how long the mix sits before it is used. Those are the parts of the Stihl chainsaw gas mix that people actually get wrong, and they are what the rest of this page covers.
Stihl chainsaw fuel ratio by model
These are the current MS saws we checked against Stihl’s own product pages for the 2-stroke mix ratio statistics, smallest engine first. Displacement is Stihl’s published figure; the ratio comes from Stihl’s brand-wide statement, because Stihl does not print a separate ratio on each product page.
| Model | Class | Engine | Fuel ratio | Oil per US gallon |
|---|---|---|---|---|
| MS 172 | Homeowner | 31.8 cc | 50:1 | 2.56 oz |
| MS 180 | Homeowner | 31.8 cc | 50:1 | 2.56 oz |
| MS 182 | Homeowner | 35.8 cc | 50:1 | 2.56 oz |
| MS 250 | Homeowner / occasional | 45.4 cc | 50:1 | 2.56 oz |
| MS 271 | Farm and ranch | 50.2 cc | 50:1 | 2.56 oz |
| MS 291 | Farm and ranch | 55.5 cc | 50:1 | 2.56 oz |
| MS 362 C-M | Professional | 59 cc | 50:1 | 2.56 oz |
| MS 462 C-M | Professional | 72.2 cc | 50:1 | 2.56 oz |
| MS 500i | Professional | 79.2 cc | 50:1 | 2.56 oz |
If your saw is not in the table, the answer is still 50:1. That includes the MS 170, the MS 194 T and MS 201 T top-handle saws, the Farm Boss variants and the older 0-series saws (the 029, 036, 044 and their relatives) when you run them on a current Stihl oil. The only exception worth knowing about is the oil, covered below: older Stihl manuals gave a different ratio for other brands of oil than for Stihl’s own bottle.
The same can also runs every other Stihl gasoline tool you own. Stihl’s trimmers, KombiEngines and blowers are 50:1 as well, 4-MIX engines included; the Stihl weed eater gas mix guide has those models.
How much oil for each can
Stihl sells its oil in bottles sized for one US gallon of gas at 50:1, so the one-gallon batch needs no measuring at all. For bigger cans or metric amounts:
| Gas | Stihl oil at 50:1 |
|---|---|
| 1 US gallon | 2.56 oz (one 2.6 oz bottle) |
| 2 US gallons | 5.12 oz |
| 2.5 US gallons | 6.4 oz |
| 5 US gallons | 12.8 oz |
| 1 litre | 20 ml |
| 5 litres | 100 ml |
| 10 litres | 200 ml |
A 5 gallon can is usually the wrong size for a homeowner saw. An MS 180 or MS 250 tank holds well under a litre, and Stihl’s storage limit on pump-gas mix is 30 to 60 days, so a 1 gallon or 2.5 gallon can mixed fresh each month is what keeps the carburettor clean. Professionals running an MS 462 for a full day are the people who empty a 5 gallon can before it ages.
For an amount that is not in the table, the calculator below is preset to 50:1:
Which oil goes in a Stihl chainsaw
Stihl sells three 2-stroke oils, HP, HP Super and HP Ultra, and all three mix at the same 50:1 in Stihl saws. The difference is the base oil and how cleanly it burns, not the amount you pour: the Stihl 2-stroke oil guide compares them. Stihl’s fuel FAQ recommends HP Ultra for maximum performance and engine life.
You do not have to use Stihl’s bottle. A quality oil for air-cooled 2-stroke engines rated JASO FD or ISO-L-EGD at 50:1 gives the saw what Stihl designed it for; Husqvarna XP+, Echo Power Blend X and Echo Red Armor all carry the JASO FD rating, so read the back label for the rating rather than the brand on the front. Two oils do not belong in a saw at any ratio: TC-W3 outboard oil, which is formulated for water-cooled engines that run far cooler, and ordinary 4-stroke motor oil, which does not burn cleanly and fouls the plug and exhaust. The TC-W3 vs JASO FD guide explains the difference.
The older-saw exception
Stihl’s ratio was not always the same for every bottle. Older Stihl manuals gave 50:1 for Stihl’s own oil and a richer ratio for other brands of 2-stroke oil, because the cheaper oils of that era could not protect an engine at 50:1. Forum answers quoting 40:1 or 25:1 for a Stihl 028 or 036 often come from that second line of the manual, not from a different engine design.
The practical rule for an old saw: with Stihl oil or another JASO FD oil, mix 50:1. With an unrated or unknown oil, mix richer, and 40:1 (3.2 oz per gallon) is the cautious figure. Too much oil costs you some smoke and a dirtier spark arrestor; too little costs you a piston. The 40:1 vs 50:1 guide works through the trade-off and how to convert a can you already mixed.
Which gas goes in a Stihl chainsaw
The gas half of the mix matters as much as the oil half, and Stihl is specific about it:
- Octane: unleaded of at least 89 octane (mid-grade in the US). Low octane raises cylinder temperature, and a saw at full throttle in a cut is already the hottest thing in the shed.
- Ethanol: up to 10 percent. Stihl’s fuel FAQ says all its gasoline engines can use E10 and must not use E15; fuel above 10 percent ethanol can damage the saw and may void the warranty. That rules out the cheap E15 pump at some stations.
- Freshness: Stihl’s fuel FAQ says not to store or use mix older than 60 days, and preferably no longer than 30 days, even with a stabilizer. Its US mixing guide says storage should never exceed three months. The stricter figure is the safer one to plan around.
Ethanol is the reason for the short shelf life. It pulls water out of humid air, and in a vented can the mix slowly takes on water and separates. A saw that sits all summer with last autumn’s mix in the carburettor is the classic no-start in the spring startup guide.
MotoMix or mixing your own
Stihl MotoMix is Stihl’s canned premix: ethanol-free gas already mixed at 50:1 with HP Ultra. Stihl gives it a storage life of up to two years and says it can be left in the machine during seasonal storage, which pump-gas mix cannot. The cost is the price: canned premix costs several times what the same gallon of self-mixed fuel does. For a saw that runs a few tanks a year, MotoMix removes the stale-fuel problem for the price of a few cans. For a saw that empties a gallon a day, mixing your own is cheaper and the fuel never gets old enough to matter. The premixed 2-stroke fuel comparison puts MotoMix, TruFuel and mixing your own side by side.
Mixing it right
- Use an approved fuel can, sized to what you burn in a month.
- Pour the oil in first, then the gas, so the gas stirs the oil as it goes in.
- Close the can and shake it, and shake it again before every fill: the oil does separate slowly.
- Write the date on the can. It is the only way to know when the 30 days are up.
- Before storage, run the saw dry or fill it with MotoMix. Stihl’s long-term storage advice is to empty the tank and run the engine at idle until it stops; the winterizing guide has the rest of the routine.
The short version
Every Stihl chainsaw takes 50:1. Use one 2.6 oz bottle of Stihl or another JASO FD oil per US gallon of fresh 89+ octane gas with no more than 10 percent ethanol, mix only what you will burn within 30 days, and run the saw dry before it sits. For other brands of saw the chainsaw gas oil ratio page has Husqvarna, Echo and the older 40:1 saws, and the 50:1 page has the full chart in gallons and litres.
Common questions
[01] What is the fuel ratio for a Stihl chainsaw?
50:1 for every current Stihl gasoline chainsaw, from the MS 172 to the MS 500i: 50 parts gas to 1 part 2-stroke oil. That is 2.56 fl oz of oil per US gallon, or 20 ml per litre (100 ml in a 5 litre can). Stihl sets the ratio brand-wide rather than per model.
[02] How much Stihl oil do I put in a gallon of gas for my chainsaw?
One 2.6 oz bottle of Stihl 2-stroke oil per US gallon of gas. The bottle is sized for exactly that: 2.56 oz rounds to 2.6. For a 2.5 gallon can use 6.4 oz, and for 5 gallons 12.8 oz.
[03] Can I use non-Stihl oil in a Stihl chainsaw?
Yes, a quality air-cooled 2-stroke oil rated JASO FD or ISO-L-EGD, mixed at 50:1. Do not use TC-W3 outboard oil or 4-stroke motor oil. Older Stihl manuals gave a richer ratio for other brands of oil than for Stihl's own, so on an old saw with an unrated oil, 40:1 is the cautious choice.
[04] What gas should I use in a Stihl chainsaw?
Unleaded gas of at least 89 octane with no more than 10 percent ethanol. Stihl's fuel FAQ says its engines can use up to E10 and must not run E15. Ethanol-free gas or Stihl MotoMix avoids the ethanol question entirely.
[05] How long is Stihl chainsaw mix good for?
Stihl's fuel FAQ says not to use mix older than 60 days, and preferably no older than 30, even with a stabilizer. Stihl MotoMix, the canned premix, is the exception: Stihl gives it a storage life of up to two years and says it can be left in the saw during seasonal storage.