Gas oil mix ratio calculator
How much oil to add to petrol at a 1:N ratio.
Fill in the fields and the result will appear here automatically.
Calculates oil for a petrol volume and a 1:N volume ratio: one part oil to N parts petrol. It also shows nominal combined volume and the oil share of the mixture. The N = 20–100 range is a product limit, not a recommendation for every engine. Choose the ratio, oil, petrol and storage conditions from the particular engine and product instructions.
How it works
Formula and logic
Oil in mL = 1000·petrol in L/N. Nominal total in L = petrol·(1 + 1/N); oil share = 100/(N + 1)%. Adding volumes is an additive-volume assumption, not a measured final mixture volume. Petrol is positive and N is from 20 to 100; unrepresentable results are rejected.
Example
Five litres of petrol at 1:50 needs 100 mL of oil; the nominal volume sum is 5.1 litres.
Fields and units
- Petrol, L — L
- Ratio 1:N — unitless
How to use
- — Check the engine instructions for its required ratio, oil and petrol.
- — Enter a positive petrol volume in litres and N for 1:N, within this tool’s 20–100 range.
- — Measure the displayed oil in mL; follow the applicable preparation and storage instructions.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- STIHL: mix preparation under the particular engine manual, not a universal ratio STIHL 4-MIX: four-stroke principle using a petrol-oil mixture STIHL: product-specific ethanol and storage limits; ordinary fuel and MotoMix differ
- Limitation
- Check the engine instructions for its required ratio, oil and petrol. Adding volumes is an additive-volume assumption, not a measured final mixture volume.
FAQ
What happens with too much oil?
Do not alter the manufacturer’s specified ratio to “protect” an engine. Extra oil changes the mixture and operating conditions; the tool only measures the chosen proportion and does not assess compatibility or consequences.
Why is the oil share not exactly 2 % at 1:50?
Because the ratio is stated against the petrol while the share is measured against the finished mixture. 1000 ml of petrol takes 20 ml of oil, but the mixture is 1020 ml, and 20/1020 gives 1.96 %.
Can the mixture go into a four-stroke engine?
Use the particular engine’s instructions. Engines with a separate oil system and engines lubricated by a fuel mixture require different arrangements. STIHL 4-MIX, for example, uses a four-stroke principle with a petrol-oil mixture; stroke count alone does not decide this.
Is petrol with ethanol suitable?
The engine and fuel manufacturers specify ethanol compatibility and storage life. STIHL’s instructions for ordinary petrol and ready-mixed MotoMix, for example, differ. This tool gives no universal one-month storage limit or ethanol allowance for every machine.