What’s the Fuel Mixture for a Stihl Chainsaw (3 Ratios)
For a gasoline-powered STIHL chainsaw, use a 50:1 fuel mix only when the model’s manual calls for it: 1 US gallon of fresh gasoline with 2.6 US fluid ounces of air-cooled 2-cycle oil, or 5 liters with 100 milliliters of oil. Use unleaded gasoline rated at least 89 AKI and containing no more than 10% ethanol in the US.
Fuel ratios can look like a small detail beside engine size and bar length, but the wrong mix can damage a saw. The reliable starting point is the fuel specification for your exact model, not a general rule, a bottle label, or a ratio used for another brand.
In my equipment review work, I often see confusion between 50:1, 40:1, and 32:1. The numbers describe how much gasoline is used for each part of oil by volume. Below, I explain the three ratios, show the measured quantities, and give a careful mixing and fueling routine. Always let your STIHL manual and fuel-cap label settle any model-specific question.
Confirm the STIHL Model, Fuel Ratio, and Safety Setup
A fuel ratio states the volume of gasoline compared with the volume of 2-cycle oil. Many gasoline-powered STIHL chainsaws specify 50:1, but the exact model’s manual takes priority. Check the model name and fuel label before mixing; battery saws do not use this fuel, and 4-MIX equipment has its own instructions.
How the three ratios compare
The standard mix for a STIHL chainsaw is 50:1 when its manual specifies it. That means 50 equal volume parts gasoline to 1 part oil. The examples below use US fluid ounces and US gallons, so do not treat them as imperial measurements.
| Ratio | Oil per 1 US gallon gasoline | Oil per 5 L gasoline | How to use it |
|---|---|---|---|
| 50:1 | 2.6 US fl oz | 100 mL | Use for a STIHL model whose manual specifies 50:1 |
| 40:1 | 3.2 US fl oz | 125 mL | Not a substitute for 50:1 |
| 32:1 | 4.0 US fl oz | 156 mL | Not a substitute for 50:1 |
The 40:1 and 32:1 figures are shown because they are often discussed, not because they are approved alternatives for a saw that calls for 50:1. Adding more oil does not make an unapproved mix safer. It can increase smoke and deposits, while the wrong mix can affect how the engine runs.
Check the fuel and oil
Use fresh, unleaded gasoline with an octane rating of at least 89 AKI, STIHL’s minimum recommendation. In the US, do not use gasoline with more than 10% ethanol. Choose quality 2-cycle engine oil rated for air-cooled engines; STIHL recommends its own oil. Follow the manual if it gives a more specific fuel instruction.
Before you measure, confirm the saw is gasoline-powered and identify the exact model. Do not assume a similar-looking saw uses the same instructions. A model’s chain pitch, gauge, drive-link count, bar length, idle speed, and maximum engine speed also depend on its own markings and manual. Fuel ratio does not tell you those specifications.
If the manual or cap label is missing or unclear, find the model number and get the correct STIHL documentation before fueling. Do not guess, and do not use straight gasoline. Key takeaway: verify the exact model first, then use its stated ratio.
Mix Fuel and Operate the Saw Safely
Good mixing starts with accurate measurement and a clean, approved fuel container. Measure both liquids by volume, blend them thoroughly, and label the container. Then fuel and start the saw according to its manual. A correct ratio matters, but safe handling and a sound saw matter too.
Step-by-step mixing and fueling
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Prepare the work area and saw. Wear suitable chainsaw personal protective equipment (PPE). Before starting, inspect the chain brake, chain tension, bar, chain catcher, and controls. Check the work area, escape route, and overhead hazards. For tree work, follow applicable OSHA requirements and ANSI Z133 practices.
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Measure the gasoline and oil. For 1 US gallon of gasoline, measure 2.6 US fluid ounces of oil for a 50:1 mix. For 5 liters of gasoline, measure 100 milliliters of oil. Use a marked measuring tool rather than estimating a pour.
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Blend in an approved container. Add the measured oil to fresh gasoline in an approved fuel container, then mix thoroughly. Label and date the blend so you can identify it later. Follow STIHL’s instructions for how long mixed fuel may be kept; avoid storing it in the saw’s tank.
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Fuel and start with care. Refuel outdoors, away from ignition sources. Never refuel a hot saw. Follow the model’s cold- or warm-start steps, and start the saw on stable ground. Keep both hands on the saw. Engage the chain brake when appropriate, and cut only with a sharp, correctly tensioned chain.
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Stop if the saw behaves abnormally. If it overheats, loses power, or runs poorly, stop work and investigate. Do not try to solve a problem by adding oil beyond the manual’s specified ratio.
These checks do not replace the manual or proper chainsaw training. Avoid the guide-bar nose, which can cause kickback. Keep control of the saw, and do not cut with a dull, loose, or damaged chain. Key takeaway: measure the mix, follow the start procedure, and stop if the saw’s behavior changes.
Practical mixing examples
These examples show how to prepare common amounts for a model specified for 50:1. Use a dedicated measure, and check your container markings. The gasoline amount is the base amount; the oil quantity is added to that gasoline.
| Gasoline | 50:1 oil amount | Useful for |
|---|---|---|
| 1 US gallon | 2.6 US fl oz | A typical small batch |
| 2 US gallons | 5.1 US fl oz | A larger batch |
| 5 L | 100 mL | Metric measurement |
| 10 L | 200 mL | Metric measurement |
These are calculated volume examples, not a recommendation to mix more fuel than you expect to use. A smaller, freshly mixed batch can reduce the chance that fuel sits unused. Keep the container sealed and stored safely as directed by the fuel and saw instructions.
Maintain, Sharpen, and Inspect the Chainsaw
Fuel ratio is one part of engine care, not a fix for every performance problem. A dull chain, incorrect tension, a blocked air intake, or a fuel-system issue can also affect operation. Inspect the saw as its manual directs, and do not change the mix to compensate for a fault.
After shutting down, let the saw cool before cleaning or refueling. Check for leaks or damage, and clean the air intake and cutting system as directed in the manual. Keep the chain sharp and correctly tensioned. Use the model-specific guide bar and chain specifications rather than inferring them from another saw or its fuel ratio.
One serious risk is a lean seizure: an engine may run too hot and score its piston and cylinder when it lacks proper lubrication or has a fuel-system problem. Straight gasoline contains no 2-cycle oil, so running it in a 2-cycle engine can quickly cause severe damage. Stale or contaminated fuel can also lead to poor running and harm the engine.
If the saw loses power or overheats, stop it and check the cause. The correct response is not to add extra oil unless the model’s instructions call for a different ratio. Have the fuel system or engine checked if you cannot find the problem. Key takeaway: maintain the saw and troubleshoot symptoms instead of changing a specified mix.
Store Fuel and Prepare for Seasonal Use
Mixed fuel can deteriorate, so its storage time matters. Keep it in an approved, labeled container away from heat, sparks, and open flames. Follow the storage period and seasonal instructions in the STIHL manual and fuel product directions; do not assume every blend has the same usable life.
Mark the mixing date on the container, and prepare only as much as you expect to use within the stated period. Do not keep mixed fuel in the saw’s tank for long-term storage. For seasonal storage, follow the manual’s steps for the saw and fuel system. Dispose of old or contaminated fuel through a local service that accepts it; do not pour it onto the ground or down a drain.
Before using a stored saw again, inspect it for fuel leaks or damage and follow the manual’s starting checks. If fuel looks or smells unusual, or the saw runs poorly, stop and address the fuel or equipment issue rather than adding oil to the tank. Key takeaway: date your blend, follow the stated storage limit, and keep fuel away from ignition sources.
Fuel-Mix FAQ
These short answers cover common questions about STIHL chainsaw fuel. The model’s manual remains the final reference, especially if a saw’s label, fuel type, or service history raises doubt. When instructions differ from a general example, follow the model-specific direction.
What is the fuel mixture for a STIHL chainsaw?
Use 50:1 only if the manual for your gasoline-powered STIHL chainsaw specifies it. That is 2.6 US fluid ounces of oil per US gallon of gasoline, or 100 mL per 5 liters.
How much 2-cycle oil goes in 1 gallon of gas at 50:1?
Use 2.6 US fluid ounces of air-cooled 2-cycle oil with 1 US gallon of gasoline.
How much oil goes in 5 liters of gasoline at 50:1?
Use 100 mL of 2-cycle oil with 5 liters of gasoline.
Can I use a 40:1 mix in a STIHL chainsaw?
Not if the model’s manual specifies 50:1. A 40:1 ratio uses 3.2 US fluid ounces per US gallon, which is more oil than the 50:1 mix.
Can I use a 32:1 mix in a STIHL chainsaw?
Not for a model specified for 50:1. A 32:1 mix uses 4.0 US fluid ounces per US gallon; follow the manual rather than choosing a different ratio.
Can I run a STIHL 2-cycle chainsaw on straight gasoline?
No. A 2-cycle engine needs oil mixed with its gasoline for lubrication. Straight gasoline can cause severe engine damage.
What gasoline should I use?
Use fresh, unleaded gasoline rated at least 89 AKI. In the US, STIHL advises against gasoline containing more than 10% ethanol.
Can I use any 2-cycle oil?
Use quality oil rated for air-cooled 2-cycle engines, preferably STIHL oil. Follow the model manual and oil label.
Do battery-powered STIHL chainsaws need mixed fuel?
No. Battery-powered saws use a battery, not gasoline. Follow their manual for charging and care.
What should I do if my saw runs hot or loses power?
Stop operating it and investigate the fuel, maintenance, or equipment issue. Do not try to correct the problem by adding unapproved extra oil.
The dependable rule is simple: identify the exact saw, confirm its fuel specification, and measure the mix accurately. For a model whose manual specifies 50:1, use 2.6 US fluid ounces per US gallon or 100 mL per 5 liters.
(This article was written by one of our staff writers, Marcus Thorne. Visit our Meet the Team page.)
