Gas-to-Oil Ratio Calculator
Calculate the exact two-stroke oil dose from a fuel amount, or work backward from an oil amount to the required gasoline volume.
Mix inputs
Live mix result
Oil to add
2.56 US fl oz
for 1.00 US gal of gasoline at 50:1
Excel export is ready for the current example.
Oil to add: 2.56 US fl oz.
Quick mix table
Oil required for one through five units of gasoline at the current ratio and selected units.
| Gas amount | Gas unit | Oil required | Oil unit |
|---|---|---|---|
| 1.00 | US gal | 2.56 | US fl oz |
| 2.00 | US gal | 5.12 | US fl oz |
| 3.00 | US gal | 7.68 | US fl oz |
| 4.00 | US gal | 10.24 | US fl oz |
| 5.00 | US gal | 12.80 | US fl oz |
This table is a measuring aid, not a ratio recommendation. Use the ratio specified for your exact engine and oil.
How to use this gas-to-oil ratio calculator
What this calculator does
This calculator converts a two-stroke fuel specification written as gasoline-to-oil parts, such as 50:1, into practical liquid volumes. Give it the ratio and either a gasoline amount or an oil amount; it calculates the matching quantity, the finished mixture volume, and the oil share of that finished mixture. It is a measuring and conversion tool only. It does not decide which ratio, gasoline grade, or oil specification is correct for your engine. The equipment manufacturer's manual remains the authority for that choice.
When to use it
Use it when preparing a fresh batch for a chainsaw, trimmer, blower, small motorcycle, outboard, or other two-stroke engine that requires premixed fuel; when converting a manual's metric instruction to US or Imperial volume units; when checking how much gasoline pairs with a known bottle of two-stroke oil; or when creating a small reference table for repeated mixing. Manufacturer guidance can differ by engine and lubricant, so compare your chosen ratio with the documentation for your exact model. For example, Husqvarna's fuel-mix guidance for petrol chainsaws explains its recommended ratios and cautions that small measuring errors can matter.
How to calculate
- The calculator opens with a complete demonstration: a 50:1 ratio, 1 US gallon of gasoline, and 2.56 US fluid ounces of oil. The example result and a validated Excel workbook are available immediately.
- Replace Gas-to-oil ratio with the gasoline side of your specified R:1 ratio. Type 40 for 40:1, 50 for 50:1, and so on.
- Edit either Gas (petrol) volume or Oil volume. Whichever quantity you edit most recently becomes the driving input, and the other quantity is recalculated live.
- Choose Gas unit and Oil unit as needed. Changing a unit converts the current value instead of merely changing its label. The calculator supports liters, milliliters, US gallons, US fluid ounces, Imperial gallons, and Imperial fluid ounces.
- Read the live result and the quick mix table, then use Download Excel if you want the current assumptions and calculated quantities in a workbook. Reset clears the demonstration and all semantic input data; Excel export stays disabled until a complete valid ratio plus gas or oil amount is entered again.
Input guide
- Gas-to-oil ratio is required and accepts a positive decimal number from 0.01 through 10,000. Enter only the gasoline-side number, not “50:1” as text. Example: 50. A larger number means less oil for the same gasoline amount; a smaller number means more oil. Zero, negatives, commas used as decimal separators, scientific notation, and unit text are rejected.
- Gas (petrol) volume is one of two alternative amount inputs. Enter a positive decimal with a period as the decimal separator, for example 1 when Gas unit is US gal or 5 when it is L. Editing this field makes gasoline the driver and recalculates oil. Do not paste grouping separators or unit symbols into the numeric box.
- Gas unit selects the unit attached to the gasoline amount. It is required as a unit choice, and changing it converts the current gasoline value. US and Imperial gallons are different sizes, so choose the system your source uses. NIST's SI volume guidance confirms that 1 L equals 1,000 mL and explains standard volume notation.
- Oil volume is the alternative amount input. Example: 100 with Oil unit set to mL. Editing it makes oil the driver and calculates the gasoline quantity required. It must be positive and finite; leaving both gas and oil empty gives no calculable mix.
- Oil unit controls the displayed oil measurement and converts the current oil value when changed. Use mL for fine metric dosing or fluid ounces when your measuring container is marked that way. Do not treat US and Imperial fluid ounces as interchangeable.
Output guide
Primary result says either “Oil to add” or “Gasoline required,” depending on the input you last edited. Gas volume and Oil volume restate the canonical pair in your selected units. Total mixture is gasoline plus oil, shown in the selected gas unit. Oil share of final mixture is oil divided by the combined mixture, so a 50:1 ratio is 1.96% of the finished liquid, not exactly 2% of the finished liquid. The header pills summarize the current ratio, the oil dose corresponding to one selected gas unit, and which amount currently drives the calculation. The Quick mix table lists Gas amount, Gas unit, Oil required, and Oil unit for one through five gas units. All of these are exact ratio/conversion identities subject only to displayed rounding; they are not recommendations about engine suitability.
Worked example
The opening example uses 50:1 and 1 US gallon of gasoline. One US gallon contains 128 US fluid ounces, so the oil amount is 128 ÷ 50 = 2.56 US fl oz. The final mixture is 1 + 1/50 = 1.02 US gal. Oil's share of the finished mixture is 1 ÷ (50 + 1) × 100 = 1.96%. Those values match the first rendered result, the quick table's first row, and the startup Excel workbook.
Formula and interpretation
Oil volume = gasoline volume ÷ ratio.
Gasoline volume = oil volume × ratio.
Oil share of final mixture = 1 ÷ (ratio + 1).
The first two equations require gasoline and oil to be expressed in compatible volume units; this calculator handles those conversions internally in milliliters, then returns the result in the units you selected. The distinction between “oil as a percent of gasoline” and “oil as a percent of the final mixture” is worth keeping clear: 50:1 corresponds to oil equal to 2% of the gasoline volume, while oil is about 1.96% of the combined gasoline-plus-oil volume.
Mixing and safety notes
Accurate math does not compensate for the wrong fuel specification. Check the machine manual for the prescribed ratio and oil type, measure small quantities carefully, and prepare fuel in an appropriate container. Gasoline is flammable; work away from ignition sources and follow local rules for storage and handling. In U.S. workplace guidance, OSHA describes requirements for approved containers for handling gasoline and other flammable liquids. For consumer equipment, follow the stricter instructions supplied with your engine, fuel container, and lubricant.
Common mistakes include reading a 50:1 label as 50% oil, confusing US and Imperial gallons or fluid ounces, adding the oil volume to a target “final batch” without accounting for gasoline separately, and assuming one popular ratio applies to every two-stroke engine. When in doubt, use the manufacturer's stated gasoline amount and oil dose directly as a cross-check.