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About this tool
Blend city and highway km/l into a true combined mileage using the harmonic fuel-weighted formula, plus monthly litres and cost.
The Highway vs City Mileage Estimator blends a vehicle's city and highway km/l into one combined figure using the fuel-weighted harmonic formula: combined km/l = 1 ÷ (city share ÷ city km/l + highway share ÷ highway km/l). That is the only correct way to mix the two, because the thirsty city kilometres consume a bigger share of the fuel than of the distance — averaging the two mileage numbers directly always flatters the result. It also converts the blend into litres and rupees for your monthly running distance.
Open Highway vs City Mileage Estimator on AltFTool — it loads instantly in your browser.
Enter 'City mileage (km per litre)', 'Highway mileage (km per litre)' and the 'Share of distance driven in the city (%)' — or tap a preset chip like 'EPA 55/45' or 'Mostly highway'.
Add 'Distance per month (km)' and 'Fuel price (per litre)' to turn the blend into litres and rupees.
Read the combined km/l headline, the 'Simple average (wrong method)' row showing how much it overstates economy, and the monthly fuel and cost rows, then press 'Copy result'.
Uses the harmonic fuel-weighted mean, not the misleading simple average.
Displays how much a plain average would have overstated your economy.
Converts the blended figure into monthly and yearly fuel spend at your pump price.
Use combined km/l = 1 ÷ (city share ÷ city km/l + highway share ÷ highway km/l). At 11 km/l in the city and 18 km/l on the highway with 60% city driving, that is 1 ÷ (0.6/11 + 0.4/18) = 13.03 km/l — not the 13.8 km/l a simple average suggests.
Because mileage is distance per litre, not litres per distance. Over 100 km with a 60/40 split, city driving eats 5.45 litres and highway 2.22 litres, so city driving accounts for 71% of the fuel while being only 60% of the distance. A straight average ignores that and typically overstates economy by 4-8%.
The US EPA combined label figure weights city and highway 55% to 45% by distance, computed on the same fuel-weighted basis. India's certified figure comes from the Modified Indian Driving Cycle, which has an urban and an extra-urban phase rather than two separate published numbers.
Stop-start traffic means constant acceleration from rest, long idling periods that burn fuel while covering zero distance, and low gears where the engine runs off its efficient load point. Air conditioning also draws a larger share of a small engine's output at crawl speeds.
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