Ethanol Blend Calculator

E20 is a petrol blend containing 20% anhydrous ethanol and 80% petrol by volume. It is India's national blending target, mandated under the Ethanol Blending Programme (EBP) and specified under BIS standards IS 2796 and IS 17021. E20 is sold at select fuel stations across India as part of the phased rollout that began in April 2023.

In E20, exactly 20% of the total volume is ethanol and 80% is petrol. For a 40-litre fill, that is 8 litres of ethanol and 32 litres of petrol. The blend percentage is always stated by volume, not by mass or energy content.

The number after 'E' is the percentage of ethanol by volume: E5 has 5%, E10 has 10%, E20 has 20%, and E85 has 85% ethanol. Higher blends have more ethanol and therefore lower volumetric energy content. E10 is common in many countries; E20 is India's current national target; E85 is used in flex-fuel vehicles designed to handle a wide ethanol range.

Ethanol has a lower energy density per litre than petrol — roughly 21.2 MJ/L versus 32.0 MJ/L for petrol. This is because ethanol molecules already contain oxygen, which reduces the amount of chemical energy released per litre during combustion. The more ethanol in a blend, the lower the blend's energy density, which is why higher blends generally need slightly more fuel volume to travel the same distance.

E20's theoretical energy density is 29.84 MJ/L, which is about 93.25% of pure petrol's 32.0 MJ/L — a theoretical energy deficit of roughly 6.75%. However, real-world fuel-economy loss is typically 3–4% for vehicles whose engines are optimised for the blend (ethanol's higher octane improves spark timing and partly offsets the calorific shortfall), and 6–7% for vehicles designed for pure petrol.

Multiply the total fuel volume by the ethanol percentage divided by 100 to get the ethanol litres. The petrol volume is the remainder. For example, 40 litres of E20: ethanol = 40 × 0.20 = 8 litres; petrol = 40 × 0.80 = 32 litres. The calculator does this instantly for any volume and any blend from E0 to E85.

This calculator is an educational volume and energy tool — it does not assess vehicle compatibility. Whether your vehicle can use E20 depends on the manufacturer's specification and the materials used in the fuel system. Check your vehicle owner's manual or contact the manufacturer. In India, vehicles bearing the 'E20 compatible' or 'E20 ready' designation are cleared for use with E20 fuel.

Higher ethanol blends do have lower volumetric energy content, which tends to reduce mileage. However, ethanol also has a higher octane rating (RON ~109 vs ~91–95 for petrol), which allows engines tuned for the blend to advance spark timing and recover some of the energy deficit. NITI Aayog data show that optimised E20 vehicles see only ~3–4% mileage loss rather than the ~6.75% pure-energy calculation might suggest. Older E0-designed engines see the larger ~6–7% impact.

Lower heating value (LHV), also called net calorific value, is the usable energy per litre of fuel when water produced during combustion leaves as vapour rather than condensing. Car engines exhaust hot gases, so water leaves as steam — LHV is the correct measure for comparing automotive fuels. Higher heating value (HHV) includes the energy to condense that steam and overstates what an engine can actually use.

E85 is a high-ethanol blend containing approximately 85% ethanol and 15% petrol by volume (though real-world seasonal composition can range from 51% to 83% ethanol). E85 requires a flex-fuel vehicle designed for high-ethanol operation. Its energy density is only about 71% of pure petrol at the nominal 85% blend. E85 is available in limited markets and is not part of India's current mainstream EBP rollout, which focuses on E20.

Blend energy density (LHV in MJ/L) is the volume-weighted average of the component heating values: blendLhv = (ethanolFraction × 21.2) + (petrolFraction × 32.0). For E20: (0.20 × 21.2) + (0.80 × 32.0) = 4.24 + 25.60 = 29.84 MJ/L. This linear mixing rule is mathematically exact under the ideal additive-volume assumption, and the small real-world volume contraction (<0.5%) is negligible for a consumer-education tool.

The theoretical energy figure (6.75% lower for E20) assumes the engine extracts energy from both fuels with identical efficiency. In practice, ethanol's higher octane number (around 109 RON) enables optimised engines to advance the ignition timing and run higher compression, recovering part of the calorific gap. NITI Aayog estimates optimised E20 vehicles lose only 3–4% fuel economy rather than 6.75%, while non-optimised vehicles lose 6–7%. The calculator shows the theoretical figure; always check manufacturer guidance for real-world estimates.