Chainsaw fuel: mix ratios, ethanol and fuelling distances as makers and regulators state them

This page reports what the named codes, regulators and makers say. It is not training and does not teach the work. This page reports what the official source says. It is not legal advice: ask the office named here.

The ratio and the oil for a given saw are set in that saw's own manual, and every maker page below says so. The table gives only what each maker's page states. For the arithmetic of turning a ratio into millilitres of oil, the site has a fuel mix calculator that starts empty and takes the ratio typed in. For the courses that teach saw work, see the guides on chainsaw tickets and certifications by country.

Mix ratios and fuel as three makers state them

Makers are listed alphabetically. Each row is what one web page of that maker says, with the date the page shows or the date it was read.

Maker and page	Ratio stated	Petrol and storage stated
ECHO, United States support article on engines that will not start	The ratio is the one in the operator's manual. The article gives no figure	Fresh fuel under 30 days old, rated 89 to 93 octane, free of water and debris. Fuel left in a unit for more than 60 days before storage may leave the carburettor needing work
Husqvarna, United States page on mixing two-stroke fuel (page date 2/1/2021)	The owner's manual gives the ratio. As a general guide, 50:1 for its products up to and including 75 cc, which the page converts to 2.5 fluid ounces of oil per gallon	Unleaded, ethanol-free petrol when not using premixed fuel. Mixed fuel is not stored for more than one month, and stabilizers are said to extend that to up to twelve months
STIHL, United States guide to mixing oil and gas	50:1. The page opens by saying most of its petrol equipment runs on 50:1 and later says all of it does	Mid-grade unleaded with a minimum octane rating of 89. The page recommends mixing only enough for a few days' work and says storage should never exceed three months
STIHL, United Kingdom page on the right fuel mix (dated June 26, 2025)	1 part oil to 50 parts petrol, worked out on the page as 100 ml of oil for 5 litres of petrol	Minimum 90 RON. Petrol with 5 percent (E5) or 10 percent (E10) ethanol is stated to be suitable for every STIHL chainsaw. A mix made up by the user may no longer be fit for use after 30 days of storage

The two STIHL pages are written for two markets. Husqvarna's page and ECHO's article each point to the saw's own manual for the ratio. ECHO's article lists the oil as ECHO's own brand or an oil that meets the ISO-L-EGD and JASO M345 FD performance standards. STIHL's United Kingdom page names the TC classification for the oil. Husqvarna's page describes mineral, semi-synthetic and full synthetic two-stroke oils and warns against oil made for water-cooled engines and against four-stroke oil.

Husqvarna says too much oil can make an engine hard to start and cause carbon build-up and smoke, and too little can cause internal damage and overheating. The Canadian Centre for Occupational Health and Safety says in its saw maintenance fact sheet (last revised April 24, 2024) that too much oil makes a saw run dirty and too little damages engine parts, and that the mix follows the manufacturer's recommendations.

Ethanol

The US Environmental Protection Agency page on ethanol waivers (last updated March 23, 2026) says a 1978 Clean Air Act waiver allowed 10 percent ethanol in petrol, known as E10, and that almost all petrol sold is an E10 blend. It does not mention chainsaws.

The only EPA statement found that names chainsaws is the regulatory announcement EPA-420-F-10-054 of October 2010, in an EPA snapshot archive. It reports a partial waiver for petrol with up to 15 percent ethanol (E15) for model year 2007 and newer cars, light trucks and sport utility vehicles. It says EPA was not approving E15 for nonroad engines, vehicles and equipment, and gives "lawn mowers, chainsaws and boats" as examples, because there was not enough test data. That is a 2010 statement and the page above does not repeat it for saws.

The ethanol statements the three makers print on their own pages are in the table above, each with its date and market.

Fuelling and starting distances in rules and guidance

Source	What it states about fuelling
OSHA, 29 CFR 1910.266(e)(2) and (d)(9), logging operations	The saw is fuelled at least 10 feet (3 m) from any open flame or other source of ignition, and started at least 10 feet (3 m) from the fuelling area. Each portable powered tool is shut off during fuelling
HSE, Chainsaws at work (INDG317)	Petrol containers are in good condition, clearly labelled, with securely fitting caps. An auto-filler spout reduces spillage. Fuel containers are kept well away from fires and other ignition sources, including the saw itself, with at least 4 m recommended during starting and use
WorkSafe Western Australia, chainsaws page (updated April 1, 2025)	Refuelling takes place only after the motor has cooled, in a clean area. The operator moves at least three metres from the fuelling area before starting. Containers comply with AS/NZS 2906:2001. Fuel and tools are stored at least 10 metres from where cutting happens

OSHA's 1910.266 binds employers in logging operations; its chain saw paragraph is the one that sets the distances, and OSHA treats tree care work under other standards as well, set out in the guide on OSHA standards for tree work. HSE's leaflet is guidance, and WorkSafe Western Australia's page is a state regulator's safety advice. For used oil, HSE adds that discarded engine oil is a very poor chain lubricant and may cause cancer with regular skin contact.

Other pages on the same saws: chainsaw protection and saws and cutting words.

Credit: the HSE statements are adapted from HSE publication INDG317, Crown copyright, used under the Open Government Licence v3.0.

Chainsaw fuel: mix ratios, ethanol and fuelling distances as makers and regulators state them

Mix ratios and fuel as three makers state them

Ethanol

Fuelling and starting distances in rules and guidance

Sources