Fuel mixing ratio calculator
Use this tool to calculate how much oil to add for a chosen fuel volume and ratio, or the fuel volume required for known oil.
Calculated mixture details
Calculation history, CSV and PDF
Each successful calculation is stored in the table below. You can export this history to CSV for spreadsheets or to PDF for printing and records.
| Date / Time | Fuel amount | Oil amount | Ratio (fuel : oil) |
|---|
Example fuel and oil combinations
These example values show typical mixtures for small engines when working with metric units. Use them as a quick reference alongside the interactive calculator.
| Ratio (fuel : oil) | Fuel volume (L) | Oil volume (mL) | Typical application |
|---|---|---|---|
| 25 : 1 | 5.0 | 200 | Older chainsaws, heavy duty cutting |
| 40 : 1 | 5.0 | 125 | Brushcutters, trimmers, general purpose tools |
| 50 : 1 | 5.0 | 100 | Modern chainsaws and blowers |
| 50 : 1 | 2.5 | 50 | Small premix container for occasional use |
| 100 : 1 | 5.0 | 50 | Specialised low smoke oils, light service |
Formula used in the fuel mixing ratio calculator
The calculator assumes a simple proportional relationship between fuel volume and oil volume. If the specified ratio is Rf : Ro, where Rf is the fuel part and Ro is the oil part, then:
- Oil volume = Fuel volume × (Ro / Rf)
- Fuel volume = Oil volume × (Rf / Ro)
- Total mixture = Fuel volume + Oil volume
Because the ratio is dimensionless, the same formula works for litres, US gallons, or imperial gallons. Only the units shown in the output change, not the underlying mathematical relationship.
How to use this fuel mixing ratio calculator
- Select a common preset ratio, or enter custom fuel and oil parts.
- Choose your preferred units for fuel and oil volumes.
- Enter either the intended fuel volume or the available oil volume.
- Press Calculate mixing amounts to view the exact quantities required.
- Confirm that the calculated ratio matches your engine manufacturer recommendations.
- Optionally store the result into the history table for documentation.
- Export your history as CSV or PDF for workshop records and audits.
Detailed guide to fuel mixing ratios
1. Understanding fuel mixing ratio basics
Two stroke engines rely on a precise mixture of gasoline and lubricating oil. Instead of having a separate oil reservoir, the lubricant travels with the fuel through carburetor and combustion chamber. A correct ratio keeps metal surfaces separated by a thin protective film, avoids scoring, and stabilises operating temperature during demanding work sessions. It also helps ensure reliable starting after equipment sits in storage.
2. Why accurate ratios matter for engines
Running too little oil leads to overheating, rapid wear, piston seizure, and sometimes catastrophic bearing failure. Excessive oil causes plug fouling, heavy smoke, carbon deposits, and sticky exhaust ports. A balanced compromise is essential, especially when equipment is operated under variable load, altitude, and ambient conditions throughout the working day.
3. How this fuel mixing ratio calculator works
You start by choosing a target ratio, such as 25:1, 40:1, or 50:1, then select your preferred units, litres or gallons. Enter either desired fuel volume or available oil volume. The calculator instantly returns the matching amount of the other component, total blend size, and handy conversion values for workshop notes. Clear labels beside every input guide occasional users through unfamiliar terminology.
4. Handling units, densities, and precision
The calculator assumes typical petrol and two stroke oil densities, suitable for most outdoor power tools, generators, and small motorcycles. However, advanced users can fine tune decimal places and rounding to match laboratory measurements or manufacturer documentation. This flexibility helps technicians keep records that match service logs, maintenance schedules, and warranty paperwork precisely.
5. Worked example for workshop planning
Imagine you need five litres of fuel at a 50:1 ratio for a fleet of trimmers. Enter five as the fuel volume and select fifty to one. The output shows the exact oil volume, which you can round to a convenient measuring jug mark. You can then store the result into the downloadable CSV history for future reference and auditing.
6. Related combustion planning calculators
Fuel mixing rarely exists in isolation. You might also need to analyse heat release or balance reaction equations, especially when emissions or performance are being tested. For that, you can visit the Heat of Combustion Calculator to estimate energy content, or the Combustion Reaction Calculator to design stoichiometric air–fuel mixtures under different operating scenarios.
7. Best practices when using mixed fuel
Always label containers with ratio, oil brand, and mixing date so different batches never get confused. Shake the blend thoroughly before every refill because oil may settle over time, particularly in cold conditions. Discard very old mixtures that smell stale or show separated layers. Recording each batch using the CSV or PDF outputs strengthens workshop traceability, safety, and overall quality control. This disciplined approach keeps mixed fuel consistent across operators and sites worldwide.
Frequently asked questions
1. What does a 50:1 fuel mixing ratio mean?
A 50:1 ratio means fifty parts fuel to one part oil. For every fifty litres or gallons of petrol, you add one litre or gallon of two stroke oil.
2. Can I use this calculator for premixed fuel containers?
Yes. Enter the total fuel volume you want in the container and the desired ratio. The calculator reports how much oil to add before shaking thoroughly.
3. Which units does the fuel mixing ratio calculator support?
The interface lets you work in litres, US gallons, or imperial gallons. You can switch units at any time, and the calculation automatically adjusts the required oil quantity.
4. How accurate are the results from this tool?
Results are mathematically exact for the ratio you specify. Small differences can appear in practice because of measuring jug resolution, temperature, and density variation between different fuel and oil brands.
5. What if my manual specifies a ratio not listed?
Choose the custom option and type the exact manufacturer ratio, such as 32:1 or 75:1. The calculation updates instantly, using your entered numbers instead of the standard presets.
6. Can I save or print my mixing calculations?
Yes. Each calculation can be stored in the on page history table. Use the CSV button for spreadsheet records or the PDF option for printed workshop worksheets.