Every Indian driver knows their mileage figure. Almost none of them know their cost per kilometre. Those two numbers are not the same thing, and the gap between them is where money disappears quietly, month after month.
Ask someone what their car costs and they'll quote you mileage: "15 km/l on the highway, 11 in the city." That figure measures fuel efficiency. It says nothing about what you spend per kilometre driven, which is the number you actually need when you're deciding whether to take the car or the Metro, budgeting monthly transport, or figuring out why last month's running costs spiked.
Cost per kilometre (₹/km) is a composite: fuel cost plus every other recurring expense divided by the distance you drive. Fuel is the biggest moving piece, but it's rarely more than 55–65% of the real total for a petrol vehicle driven mostly in city conditions. The rest is service, tyres, insurance, and the slow bleed of depreciation. Once you've built the full number, several things become obvious that were invisible before.
Why Mileage Alone Misleads You
Consider two identical vehicles with a claimed mileage of 14 km/l. Owner A drives 1,500 km a month on a mix of city and highway. Owner B drives 3,200 km a month, mostly highway. At ₹106/litre for petrol, Owner A spends roughly ₹11,360 on fuel per month. Owner B spends roughly ₹24,200. Their fixed costs, however, are nearly the same: insurance around ₹6,000–8,000 annually, a service every 6–10 months, tyres every 35,000–50,000 km.
Owner A's ₹/km is higher because fixed costs are spread across fewer kilometres. Owner B's is lower per km even though the monthly fuel bill is double. If Owner A is comparing the cost of driving to work versus buying a monthly Metro pass, only the ₹/km figure answers the question correctly. Mileage doesn't.
There's a second problem: mileage figures assume a fixed fuel price. Your actual fuel spending depends on when and where you fill up, how consistent your driving pattern is, and since April 2026, how your specific vehicle handles E20 petrol. As covered in this breakdown of E20 and its mileage effect, the efficiency change from the current E20 blend varies by vehicle age and calibration, typically somewhere between 1% and 7% compared to older blends. That variance alone can shift your real ₹/km meaningfully, but you'll only see it in a tank-to-tank log, not in a manufacturer mileage spec published years ago.
Building the Real Number: A Worked Example
Let's work through a concrete calculation for a mass-market petrol hatchback driven in a metro city, putting in around 1,200 km per month. These are conservative, mid-range estimates, your numbers will vary, but the structure holds for any vehicle.
Fuel cost
At 12 km/l in city traffic (realistic, not claimed) and ₹106/litre: 1,200 ÷ 12 = 100 litres per month. 100 × ₹106 = ₹10,600/month. Per km: ₹10,600 ÷ 1,200 = ₹8.83/km.
Service and maintenance
A typical service for a petrol hatchback in India runs ₹3,500–6,000 for a standard service (oil, filter, inspection) every 7,500–10,000 km, depending on the service centre. Say ₹5,000 every 8,000 km. At 1,200 km/month, that's one service roughly every 6.5 months, or ₹5,000 ÷ 8,000 = ₹0.625/km. Add minor consumables (wiper blades, coolant top-up, brake fluid) at maybe ₹1,000/year: roughly ₹0.07/km.
Tyres
A decent set of four tyres for a compact hatchback costs ₹14,000–20,000. Realistic life in Indian city conditions: 35,000–40,000 km. At ₹16,000 ÷ 38,000 km: ₹0.42/km.
Insurance
Comprehensive insurance for a 3–5 year old hatchback in a metro: roughly ₹8,000–12,000/year after no-claim bonus erosion and typical add-ons. At ₹10,000 ÷ 14,400 km/year: ₹0.69/km.
Depreciation
This is the number most people skip, and it's the most consequential. A petrol hatchback that was bought for ₹7 lakh five years ago might be worth ₹3.5–4 lakh today, depending on condition and market. That's roughly ₹60,000–75,000 of value lost per year, or at 14,400 km/year, somewhere around ₹4.50–5.20/km. For a newer or more expensive vehicle, this number is larger. For a fully depreciated beater you plan to run until it stops, it's negligible.
The total
- Fuel: ₹8.83/km
- Service + consumables: ₹0.70/km
- Tyres: ₹0.42/km
- Insurance: ₹0.69/km
- Depreciation: ₹4.80/km (mid estimate)
Total: approximately ₹15.44/km.
The mileage-only calculation gave you ₹8.83/km. The real number is 75% higher. This is not unusual. For SUVs with larger servicing bills, premium tyres, and higher fuel consumption, the full ₹/km can exceed ₹20–22 even on vehicles with reasonable mileage figures. For older vehicles where depreciation is minimal but maintenance is climbing, the numbers shift again.
CNG and Diesel: Same Structure, Different Weights
For CNG vehicles, fuel cost per km drops substantially. At ₹80/kg in a city like Delhi or Mumbai and 20–22 km/kg efficiency on a factory-fitted CNG kit, fuel cost lands around ₹3.80–4.00/km. But the CNG kit adds service requirements: valve checks, cylinder hydro-testing every 3 years (mandatory), occasional regulator servicing. Those costs are real but infrequent, so they lower the monthly cash outflow while adding lumpy periodic expenses you need to plan for.
Diesel vehicles historically had a wider fuel cost advantage that has narrowed. The gap between petrol and diesel prices has compressed over the past two years, and diesel service costs are higher: the fuel system, injectors, and DPF (on newer BS6 vehicles) add meaningful maintenance overhead. For vehicles doing 2,500+ km/month, diesel still makes economic sense. Below that, the mileage savings often don't offset the higher service bill. The ₹/km calculation is the only clean way to verify this for your specific usage.
Where Tracking Actually Breaks Down
The reason most people never build this number is that the data lives in four different places. Your fuel receipt is in your pocket (then your trash). Your service bill is a PDF WhatsApp'd from the service centre. Your insurance renewal is in your email from eight months ago. Your odometer reading is in the car. Pulling this together manually, even once, takes 20–30 minutes. Doing it monthly requires a discipline that most people don't sustain past week three.
This is a data-collection problem more than a math problem. The math is simple once you have clean inputs. The friction is in logging consistently.
Bharometer
Log fill-ups in seconds, track true tank-to-tank mileage, and see your real ₹/km, petrol, diesel, CNG, or EV.
What a Fill-Up Log Gives You That Receipts Don't
A fill-up log, maintained consistently, produces your actual tank-to-tank mileage for each fill-up: not the manufacturer figure, not a seasonal average, but what your vehicle did between this fill-up and the last one. Over several months, patterns emerge that are specific to your vehicle and your driving.
You'll see mileage drop during summer in stop-start traffic in Chennai or Hyderabad, where AC load and idling pull efficiency down 10–15%. You'll see it recover on a highway run to Pune. You'll see an anomalous dip in October when you changed tyre pressure ahead of the monsoon exit and forgot to re-inflate fully. That dip shows up as a data point, not a vague sense that something was "a bit off."
Bharometer is built around this fill-up log. You record litres, amount paid, odometer reading, and the app calculates true km/l and ₹/km for that segment. The pump-scan feature photographs the pump display and auto-fills litres, amount, and rate, which removes the main friction point (transcription errors at the pump, usually while someone is waiting behind you). Petrol, diesel, CNG (tracked in kg, with km/kg mileage), and EV are all supported. If you run a dual-fuel vehicle on both petrol and CNG, both are tracked in the same log.
The monthly spending view shows total fuel spend and cost per kilometre for the period, which is exactly the input the ₹/km calculation above needs for its fuel line. You can cross-reference this against the methodology for calculating fuel cost per km to make sure you're reading the numbers correctly.
City-level daily fuel prices are available inside the app, so if you fill up in Bengaluru on a day the price moved, the log reflects the actual rate you paid rather than a stale figure.
Turning the Number Into Decisions
Once you have three to four months of clean fill-up data, plus a rough sense of your annual service and tyre costs, the ₹/km figure becomes a practical decision tool.
The Metro or cab question: if your full ₹/km including depreciation is ₹16 and a point-to-point cab is ₹14/km, and you're also paying for parking at ₹40/hour, the cab is cheaper for short trips in dense traffic. For 25+ km commutes where parking is free, the car wins clearly. The number tells you where the crossover is.
The second-vehicle question: a family considering a second car is often comparing the EMI and running cost of a new vehicle against the incremental cost of using cabs or autos for the overflow trips. The ₹/km of a new vehicle at their likely usage (say, 800 km/month) is often ₹18–22/km all-in. If the cab usage they're trying to replace is costing ₹8–10/km, the second car is not the efficient choice, whatever the showroom salesperson's "EMI from ₹7,999" framing suggests.
The CNG retrofit question: a retrofit kit adds ₹60,000–80,000 in capital cost and drops fuel cost from ₹8.50/km to ₹4.00/km. At 1,200 km/month, that's a ₹4.50/km saving, or ₹5,400/month. Payback on the kit cost: 11–15 months. But if your vehicle is already 8–10 years old and approaching replacement, the payback horizon may extend past the vehicle's useful life. The ₹/km framework shows you this clearly; a mileage figure doesn't.
For a deeper look at how to calculate true tank-to-tank mileage correctly (not the trip computer reading, which flatters most vehicles by 8–12%), the step-by-step mileage calculation guide walks through the method.
A Note on Monthly Budgeting
Most household budgets treat "fuel" as the vehicle line item. The actual vehicle line item is fuel plus service plus tyres plus insurance plus the depreciation cost of owning rather than investing that capital elsewhere. For a mid-range petrol SUV driven 1,500 km/month in a metro, this total can easily reach ₹22,000–26,000/month. That is a meaningful share of a household's disposable income, and it deserves the same tracking discipline as rent or groceries.
The mileage number is not the cost. It's one input into the cost. Build the full figure once, revisit it when a major expense changes (new tyres, insurance renewal, E20's effect on your specific vehicle's efficiency), and you'll have a clearer picture of what your car actually demands from your budget each month.