Review Information
- Reviewed by: Jack Beurge
- Review type: Research-based review
- Testing status: Not personally tested by SAWOFF — based on manufacturer documentation and reputable external sources
- Published: April 11, 2026 · Updated: July 20, 2026
Information in this review is labeled as one of four types: 🧪 SAWOFF hands-on test, 🏭 manufacturer specification, 📚 research from reputable sources, or 🧠 editorial assessment. See our testing methodology and editorial policy.
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Getting your chainsaw fuel mix ratio wrong is one of the fastest ways to destroy an engine. Too lean and you’ll seize the piston. Too rich and you’ll foul plugs, clog the exhaust, and lose power.
This guide gives you the exact measurements for every ratio, a brand-by-brand reference, and the truth about ethanol — the biggest hidden enemy of chainsaw carburetors.
The Two Ratios You’ll Encounter
Almost every chainsaw you’ll buy today uses one of these two ratios:
| Ratio | Oil per 1 US Gallon | Oil per 1 Litre | Who Uses It |
|---|---|---|---|
| 50:1 | 2.6 fl oz (77 ml) | 20 ml | Stihl, Husqvarna, most modern saws |
| 40:1 | 3.2 fl oz (96 ml) | 25 ml | Older Echo saws, some vintage models |
| 32:1 | 4.0 fl oz (118 ml) | 31 ml | Very old/vintage saws (pre-1990s) |
Always check your owner’s manual first. The correct ratio for your specific model overrides any general advice.
Exact Measurements: 50:1 Ratio Reference Table
The most commonly used ratio. Here’s how much 2-stroke oil to add for different fuel quantities:
| Gasoline Amount | 2-Stroke Oil to Add |
|---|---|
| 1 US Gallon (3.785 L) | 2.6 fl oz (77 ml) |
| 2 US Gallons (7.57 L) | 5.2 fl oz (154 ml) |
| 5 US Gallons (18.9 L) | 12.8 fl oz (379 ml) |
| 1 Litre | 20 ml |
| 5 Litres | 100 ml |
Exact Measurements: 40:1 Ratio Reference Table
| Gasoline Amount | 2-Stroke Oil to Add |
|---|---|
| 1 US Gallon (3.785 L) | 3.2 fl oz (96 ml) |
| 2 US Gallons (7.57 L) | 6.4 fl oz (189 ml) |
| 5 US Gallons (18.9 L) | 16 fl oz (473 ml) |
| 1 Litre | 25 ml |
| 5 Litres | 125 ml |
Brand-by-Brand Fuel Mix Reference
| Brand | Recommended Ratio | Recommended Oil | Notes |
|---|---|---|---|
| Stihl | 50:1 | Stihl HP Ultra Synthetic | M-Tronic saws are especially sensitive to ethanol |
| Husqvarna | 50:1 | Husqvarna XP Synthetic | Use with ethanol-free gas only |
| Echo | 50:1 (new) / 40:1 (pre-2003) | Echo Red Armor | Check year of manufacture |
| Makita | 50:1 | Makita 2-Stroke Oil | — |
| Poulan | 40:1 | Generic JASO FD oil | Older, budget-tier engines |
| Worx / Greenworks | 40:1 | Generic JASO FD oil | Check manual — some models vary |
Gasoline Quality: What You Must Know About Ethanol
This is the most important and most overlooked part of chainsaw fuel mixing.
Why Ethanol Destroys Chainsaws
Most pump gasoline in the US contains 10% ethanol (E10) or up to 15% (E15). This is catastrophically bad for small 2-stroke engines:
-
Ethanol Absorbs Water: It is hygroscopic — it pulls moisture from the surrounding air into your fuel. This causes phase separation, where the water-ethanol layer sinks to the bottom of the tank. Your engine then runs on pure water. Instant death.
-
Ethanol Dissolves Rubber: The diaphragms, gaskets, and O-rings inside small carburetors are not rated for high-ethanol fuels. Within one season of E10 use, these components harden, crack, and fail — causing your saw to refuse to start.
-
Ethanol Leaves Varnish: As ethanol-blended fuel degrades (which happens in as little as 30 days), it deposits a sticky brown varnish inside the carburetor’s tiny jets and passages. The main jet can be completely blocked by a deposit no thicker than a human hair.
The Solution: Always Use Ethanol-Free Gas
Look for “Rec-90” or “ethanol-free premium” at your local marina, farm supply store, or select gas stations. It’s slightly more expensive but will save you $80°$150 in carburetor repairs each season.
Alternative: Pre-mixed alkylate fuel cans (Stihl MotoMix, Husqvarna XP Pre-Mix) are 100% ethanol-free, pre-mixed at 50:1, and rated for 2+ year shelf life. Perfect for occasional-use chainsaws.
How to Mix Fuel Correctly
- Start with the oil. Always add oil to the mixing container first, before the gasoline. This ensures the oil is properly diluted throughout the fuel.
- Use a calibrated mixing container. Never eyeball it. A $5 ratio-marked mixing bottle (e.g., Stihl, Husqvarna, or Echo brand) gives you exact measurements every time.
- Shake the container. Mix the oil and gas thoroughly before pouring into your saw.
- Use within 30 days. Mixed fuel degrades fast. Add fuel stabilizer (Stihl Fuel Stabilizer, or Star Tron) if storing longer.
- Never use E85 or flex-fuel. These will destroy the carburetor immediately.
Chainsaw Bar and Chain Oil — A Different Product
Bar and chain oil is not mixed with fuel. It is a separate, heavier weight lubricant that feeds through the automatic oiler to the bar rail, lubricating the chain as it cuts.
- Use dedicated bar and chain oil (or clean motor oil in a pinch — SAE 30 in summer, SAE 10 in winter).
- Never use waste motor oil — it’s full of metal particles and combustion byproducts that will destroy the bar rail.
- Check the bar oil reservoir every tank of fuel.
Quick Summary
- Most modern saws: 50:1 ratio — 2.6 fl oz oil per 1 US gallon
- Some older saws: 40:1 ratio — 3.2 fl oz oil per 1 US gallon
- Always use: 89+ octane, 100% ethanol-free gasoline
- Always use: High-quality synthetic JASO FD-rated 2-stroke oil
- Never use: E10/E15 pump gas, car motor oil, or E85
- Shelf life: Use mixed fuel within 30 days, or use pre-mixed alkylate
More Maintenance Reading:
Get out there and cut. Safely.
Frequently Asked Questions
What is the standard chainsaw fuel mix ratio?
Most modern chainsaws use a 50:1 ratio — 2.6 fl oz (77ml) of two-stroke oil per 1 US gallon of gas. Older saws and some Echo models may use 40:1 — 3.2 fl oz (96ml) per gallon. Always check your owner's manual first.
What happens if I use too much oil in my chainsaw?
Too much oil (rich mix) causes excessive smoke, fouled spark plugs, carbon buildup in the exhaust port, and power loss. The saw may also be harder to start.
What happens if I use too little oil in my chainsaw?
Too little oil (lean mix) causes the engine to run hot, wear the cylinder walls and piston rings prematurely, and ultimately seize the engine. This is catastrophic and often unrepairabe.
Can I use car motor oil for chainsaw fuel mix?
No. Car motor oil contains detergents and additives designed for 4-stroke engines that will foul the spark plug and damage the piston rings in a 2-stroke engine. Always use dedicated 2-stroke oil.
Does the ratio change for different brands?
Generally no — most modern chainsaws from Stihl, Husqvarna, Echo, and others use 50:1. However, older Echo models specifically recommend 40:1. Some vintage saws from the 1970s-80s used 32:1. Always confirm with your manual.
How long does mixed chainsaw fuel last?
Mixed fuel degrades in as little as 30 days, especially if it contains ethanol. Use fresh mix within 30 days or add a fuel stabilizer to extend shelf life to 90 days. Pre-mixed alkylate fuel (like Stihl MotoMix) lasts up to 2 years unopened.
