How Much Petrol Is Actually Costing You Every Month
By the QuickYield Team · Published September 15, 2026 · 4 min read
1,000 km a month at 15 km/l and ₹100/litre petrol costs ₹6,667 a month — ₹80,000 a year, working out to ₹6.67 per kilometre. Most drivers know roughly what they spend at the pump each visit, but rarely add it up into a real monthly or annual figure — and the number that actually matters for comparing vehicles or planning a budget is cost per kilometre, not the size of each fill-up.
The formula
Monthly petrol cost = (monthly distance ÷ mileage) × price per litre. Cost per km, the more useful number for comparisons, is simply price per litre ÷ mileage — which means mileage has an outsized effect on your real running cost, more than most people intuitively expect.
Cost per km, by mileage
At ₹100/litre petrol, driving 1,000 km a month:
| Mileage | Cost per km | Monthly cost (1,000 km) |
|---|---|---|
| 10 km/l | ₹10.00 | ₹10,000 |
| 15 km/l | ₹6.67 | ₹6,667 |
| 20 km/l | ₹5.00 | ₹5,000 |
| 25 km/l | ₹4.00 | ₹4,000 |
The gap between 10 km/l and 20 km/l isn’t a rounding difference — it’s double the monthly fuel bill for the same driving. This is exactly why real-world mileage (checked from your own fill-ups over a month, not the manufacturer-claimed figure) matters so much more than most buyers weigh it against a vehicle’s purchase price.
Use your real mileage, not the claimed one
Manufacturer mileage figures are measured under controlled test conditions and are almost always higher than what you’ll see in real city or mixed driving — traffic, AC use, and driving style typically bring real mileage down 15-25% below the claimed figure. Track your own: divide the distance since your last full tank by the litres needed to fill it again, over 2-3 fill-ups for a stable average, and use that number rather than the claimed one for a realistic monthly estimate.
Enter your own distance, mileage, and petrol price into our Petrol Expense Calculator for your exact monthly and annual cost.
Frequently asked questions
›How do I find my car’s real mileage?
Fill your tank completely, note the odometer reading, drive normally until the tank is nearly empty, then fill it again and note the litres needed — distance driven ÷ litres used gives your real mileage. Average over 2-3 fill-ups for a stable number.
›Why is real mileage usually lower than the claimed figure?
Manufacturer figures come from standardized test conditions that don’t reflect real traffic, AC usage, or driving style — real-world mileage is commonly 15-25% below the claimed number for most vehicles.
›Does petrol price change enough to matter for monthly budgeting?
Yes — petrol prices in India do fluctuate over months, and even a ₹5-10/litre swing meaningfully changes your monthly cost at typical driving distances, so it’s worth revisiting this calculation periodically rather than budgeting off a one-time estimate.
›Is diesel cheaper than petrol per km?
Usually yes, since diesel is typically priced lower per litre and diesel engines often deliver higher mileage — see our Diesel Expense Calculator guide for the direct comparison.
Try it yourself
Open the Petrol Expense Calculator →
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This article is for general information only and isn’t financial, tax, or legal advice. See our disclaimer.