What does a 50:1 ratio mean?

50:1 means 50 parts gasoline to 1 part 2-stroke oil by volume. For every 50 mL of gas you add 1 mL of oil. This is the most common ratio for modern, low-emission 2-stroke engines such as newer chainsaws and string trimmers.

How do I know what ratio my engine needs?

Check the owner's manual or the label on the engine. Common ratios are 50:1 (modern chainsaws, trimmers), 40:1 (outboard motors, some dirt bikes), 32:1 (older equipment), and 25:1 (older or high-performance 2-strokes). When in doubt, use 50:1 for newer equipment.

Does the octane rating of the gas matter?

Yes. Most 2-stroke engine manufacturers recommend premium unleaded (91 octane or higher) to prevent pre-ignition (knock). Ethanol content is also important — avoid gasoline with more than 10% ethanol (E10) and never use E15 or E85, as higher ethanol concentrations can damage fuel lines and carburetors.

What happens if I use too much oil?

Excess oil causes carbon build-up on the piston and spark plug, excessive exhaust smoke, and reduced power. The engine will still run but will require more frequent spark plug changes. A slightly rich mix (e.g. 40:1 instead of 50:1) is preferable to a lean mix when in doubt.

Can I use car engine oil for 2-stroke premix?

No. You must use oil specifically labeled "2-stroke" or "2-cycle." Car engine oil (designed for 4-stroke engines) does not burn cleanly and will foul the plug, clog the exhaust port, and leave heavy deposits. Use a quality TC-W3 (for water-cooled engines) or ISO-L-EGD / JASO FD rated oil.

Does premixed fuel expire?

Yes. Standard pump gas with ethanol begins to degrade within 30 days due to phase separation. Use a fuel stabilizer if storing premix longer than 30 days, and never store it for more than 90 days. Pre-packaged non-ethanol premix (such as TruFuel or Stihl MotoMix) lasts up to 2 years unopened.

Gas Oil Ratio Calculator

Enter total fuel volume and your engine's required ratio to see exactly how much 2-stroke oil to add, in both US and metric units.

Fuel Mix Settings

Unit System

Gasoline Volume

gallon

Mix Ratio (gas : oil)

: 1

Enter just the gas part, e.g. 50 for 50:1

Common Presets

Results

Enter your values and click Calculate.

Add this much oil

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Component	US	Metric

Quick Reference — Oil per 1 US Gallon

Ratio	fl oz oil	mL oil	Common use
16:1	8.0	236.6	Older outboards, some karts
24:1	5.3	157.7	Break-in period (any engine)
32:1	4.0	118.3	Older chainsaws, Husqvarna
40:1	3.2	94.6	Outboard motors, dirt bikes
50:1	2.6	75.7	Modern chainsaws, trimmers
100:1	1.3	37.9	Full-synthetic oil (some brands)

Summary

The Gas Oil Ratio Calculator determines the exact amount of 2-stroke oil to add to a given volume of gasoline for any mix ratio. Two-stroke engines in chainsaws, trimmers, outboard motors, dirt bikes, and snowmobiles require a precise premix because the oil in the fuel is the only lubrication for the crankshaft and bearings. Incorrect ratios cause seized engines (too little oil) or fouled spark plugs and excessive smoke (too much oil). All math runs in your browser — nothing is sent to a server.

How it works

Select your unit system — US gallons/fluid ounces or metric liters/milliliters.
Enter the total amount of gasoline you want to mix.
Enter the mix ratio your engine requires (e.g. 50 for 50:1), or pick a common preset.
Click Calculate to see the exact oil volume to add.
The results table shows final mixture volume, gas amount, and oil amount.
Use the preset buttons for the most common small-engine ratios.

Use cases

Mixing fuel for chainsaws, string trimmers, and leaf blowers.
Preparing premix for dirt bikes and ATVs with 2-stroke engines.
Calculating oil amounts for outboard boat motors.
Fueling snowmobiles and jet skis that require premix.
Checking the correct ratio for a new tool before the first use.
Converting a ratio requirement between US and metric volumes.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu