Estimate the fuel cost for a trip based on distance, mileage and fuel price.
Fuel needed = distance ÷ mileage. Cost = fuel needed × price per unit.
A fuel cost estimate is only as accurate as the mileage figure feeding it, and this is where most people quietly overestimate their own savings or underestimate a trip's real cost: plugging in the ARAI-certified mileage rather than your actual real-world figure typically understates the true fuel cost by 15-25% in normal Indian driving, and by as much as 20-40% in heavy city traffic. Since fuel cost scales directly and linearly with consumption (unlike MPG-style distance-per-fuel figures), a 20% mileage overestimate translates into a genuine 20% underestimate of what a trip or month of driving will actually cost — not a rounding error.
For anything beyond a rough one-off estimate, it's worth using a mileage figure derived from your own fuel-fill records (total distance covered divided by fuel actually purchased over several tank-fills) rather than the certified figure, since your real number already bakes in your specific driving conditions — city traffic, AC use, typical load, road quality — that no generic figure can capture. Fuel prices themselves also vary meaningfully by state (due to differing state VAT/cess rates in India) and change frequently, so a cost estimate is really only as current as the fuel price you last checked; for regular budgeting, it's worth revisiting the price input periodically rather than treating one number as permanently accurate.
Your actual real-world mileage, if you have it — ARAI figures come from controlled lab conditions and typically overstate real efficiency by 15-25% in normal driving, sometimes more in heavy traffic. Using the certified figure for cost planning will systematically underestimate your real fuel spend.
Fill your tank completely, note the odometer reading, drive normally until the next full fill-up, and divide the distance covered by the fuel actually added at that second fill. Averaging this over 2-3 fill-ups smooths out any single-tank anomalies and gives a genuinely representative real-world figure for your specific driving conditions.
Because fuel is taxed by both the central government (excise duty, fixed nationally) and individual state governments (VAT and additional cess, which vary by state). This is why the same litre of petrol can cost noticeably different amounts just across a state border, even though the base pre-tax price is largely uniform.
It's only as accurate as the mileage and price figures you input — since fuel cost scales directly with consumption, a 20% error in your assumed mileage produces roughly a 20% error in the cost estimate. For budgeting purposes, using your own tracked real-world mileage and periodically updating the fuel price gives a meaningfully more reliable number than a one-time estimate with generic figures.