Two Stroke Fuel Mix Calculator
Two stroke oil dose from gas amount and mix ratio.
What it does
Two stroke engines drink oil with the gas. The mix ratio sets how much, and the right pour protects bearings without fouling the plug.
The tool above turns gas plus ratio into oil. Two gallons at 50:1 need 5.1 oz of oil, while the metric match is 7.6 L with 152 ml. Both read as one mix line for the can label.
Ratios run from rich to lean. Old manuals may call 16:1, many saws call 32:1 or 40:1, and modern trimmers often call 50:1. The cap stamp or manual rules when they disagree with habit.
Mix order matters as much as math. Oil first, half the gas, a good shake, then the rest and another shake keeps the blend even to the last tank.
Fresh fuel finishes the job. Mixed gas ages in weeks, faster with ethanol, so mix what the month needs and date the can.
How to use
- Pick imperial (gal, oz) or metric (L, ml).
- Enter gas amount.
- Pick ratio: 50:1 suits many modern tools.
- Read oil first.
- Read the full mix line next.
- Mix in a rated can and label it.
Formula
- gas
- Gasoline amount.
- ratio
- Gas parts per oil part: 16, 32, 40, or 50.
One gallon holds 128 fl oz, and one liter holds 1000 ml. The ratio reads gas parts per one oil part, so 50:1 is leaner than 32:1.
Worked example
Example: 2 gal at 50:1
Imperial defaults: 2 gal gas at 50:1. These are also the default values, so the page opens on this answer.
- Gas: 2 gal.
- Ratio: 50:1.
- Oil: 2 x 128 / 50 = 5.12 oz, shown as 5.1 oz.
- Mix: 2 gal gas + 5.1 oz oil.
- Ratio tag: 50:1.
- Tool shows 5.1 oz, 2 gal gas + 5.1 oz oil, 50:1.
Reference table
| Gas | Ratio | Oil |
|---|---|---|
| 1 gal | 50:1 | 2.6 oz |
| 2 gal | 50:1 | 5.1 oz |
| 5 gal | 32:1 | 20 oz |
| 7.6 L | 50:1 | 152 ml |
Limits
- Mix math only. Carb tuning and bar oil need separate care.
- Assumes fresh oil rated for air cooled engines.
- Old manuals override any default ratio here.
- Stale mix can harm even at the right ratio.
Common mistakes
- Guessing the ratio instead of reading the cap.
- Mixing lean to cut smoke and scoring the piston.
- Pouring freehand with no measure.
- Storing mix all season in sun.
- Fueling from an unmarked can.
Try it yourself
Quick checks. Answers sit tucked under each question.
1 gal at 50:1?
1 x 128 / 50 = 2.6 oz. Mix is 1 gal gas + 2.6 oz oil.
5 gal at 32:1?
5 x 128 / 32 = 20 oz. Mix is 5 gal gas + 20 oz oil.
Questions
How much oil for 2 gal at 50:1?
Multiply gallons by 128, then divide by the ratio. Two gallons at 50:1 need 2 x 128 / 50 = 5.1 oz.
How much oil for 7.6 L at 50:1?
Divide liters times 1000 by the ratio. Here 7.6 x 1000 / 50 = 152 ml.
Which ratio should I use?
Use the maker ratio on the cap or manual: 16:1 for old iron, 32:1 or 40:1 for many saws, 50:1 for modern trimmers.
Does exact ratio matter?
Yes. Richer than spec fouls plugs, leaner than spec starves bearings. Mix in a rated can and shake before fueling.
How do I mix?
Pour oil first, add half the gas, shake, add the rest, and shake again. Label the can with ratio and date.
Does ethanol change the ratio?
No. Ethanol free fuel stores longer, but ratio math stays the same.