Enter your fuel and oil quantities to calculate the blend ratio — the maths runs locally in your browser and nothing is uploaded.
| Distance | Fuel needed | Estimated cost | Cost / km |
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Frequently asked questions
How do I compare blends?
Pick your fuel, enter your details once, then choose 2 or 3 blends in the slots. Each blend gets its own column, and the green box tells you which is the best value and why. Change any input and every column updates instantly.
Why does mileage drop with more ethanol?
Ethanol holds less energy per litre than petrol (about 21 vs 34 MJ/L), so a litre of a high-ethanol blend moves you fewer kilometres. A small efficiency recovery offsets part of that, but higher blends still reduce range.
Can a blend with worse mileage still be cheaper?
Yes — that's the whole point of comparing. If a blend is priced low enough per litre, its lower cost can outweigh the mileage drop and give a lower cost per kilometre. The green verdict box surfaces exactly this.
Why is isobutanol only under diesel?
In this tool petrol blends use ethanol, while diesel offers both biodiesel and isobutanol as independent blend options. That keeps the petrol side simple and matches the more common real-world blends.
Are the default fuel values accurate?
They're published average energy densities and CO₂ factors, which vary by region and supplier. Edit them under Advanced settings to match your local fuel for a more precise estimate.
How the estimates are calculated
- Blend energy is the volume-weighted average of the base fuel and additive energy densities. For E20 that's 80% petrol (34.2 MJ/L) + 20% ethanol (21.1 MJ/L) = 31.58 MJ/L.
- Estimated mileage scales your pure-fuel mileage by the ratio of blend energy to the pure base fuel's energy, then applies a small blend-weighted efficiency recovery.
- Best value is decided by cost per kilometre at the single fuel price you enter, so a cheaper-burning blend can win even if it isn't the most efficient.
- Petrol blends use ethanol (E-series). Diesel blends use biodiesel (B-series) or isobutanol (IB-series) — these are independent options, so you can compare a B20 against an IB20 directly.
- Net CO₂ (lifecycle) uses well-to-wheel emission factors rather than tailpipe-only figures. Bio-derived fuels like ethanol and biodiesel have much lower net emissions because the crops reabsorb atmospheric CO₂ as they grow — so a higher-ethanol blend can cut lifecycle greenhouse gases substantially even though the tailpipe still emits CO₂. These are published average estimates and vary by feedstock and region.
- All defaults are published averages and fully editable under Advanced settings. Everything runs in your browser — nothing is uploaded.
Blending is a weighted-average problem
When two quantities with different concentrations are mixed, the final concentration depends on both concentration and volume. Equal volumes give equal weighting; unequal volumes do not.
Why percentages must be converted before arithmetic
A 20% concentration is 0.20 as a fraction. Multiplying each volume by its fraction gives the amount of the component contributed by that portion before totals are combined.