Gas Mileage Calculator
Calculate your car's fuel economy in mpg or L/100km from distance and fuel used. See cost per mile, annual fuel cost and CO2 emissions.
Between the two fill-ups (current odometer minus previous).
Fuel economy
30 mpg
7.84 L/100 km · 12.75 km/L
Annual fuel cost
$1,400
At 12,000 mi/year
Detailed results
| Metric | Value |
|---|---|
| Miles per gallon (mpg) | 30 |
| Litres per 100 km | 7.84 |
| Kilometres per litre | 12.75 |
| Fuel used | 10 gal (37.85 L) |
| Trip fuel cost | $35 |
| Cost per mile | $0.12 |
| Cost per km | $0.07 |
| CO2 emissions per year | ≈ 7,840 lbs (3,556.16 kg) |
Estimate based on distance divided by fuel used. 19.6 lbs (8.9 kg) of CO2 is released per US gallon burned. Measure over a full tank for the most reliable figure.
Last updated: July 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
With fuel prices fluctuating across India, knowing your car's real mileage helps you budget monthly fuel spend and spot problems early. Fill the tank, note the odometer reading, drive normally, then fill again and enter the litres and kilometres travelled. The calculator returns km per litre, cost per km and an estimated monthly fuel cost based on how much you drive. If mileage drops noticeably compared with earlier fills, it is often the first sign of tyre pressure issues, a clogged air filter or bad fuel. Use it before a long road trip to plan fuel stops, or monthly to track whether a new driving habit is actually saving money. Comparing your km per litre across the same routes over a few months also shows whether a servicing visit actually restored performance. Driving-school instructors and fleet managers track the same metric per vehicle to flag which car is consuming more than its peers.
How to Use This Calculator
- Step 1: Enter the distance driven in miles and the fuel used in gallons since your last fill-up.
- Step 2: Enter the price per gallon you paid at the pump.
- Step 3: Enter your approximate annual driving distance in miles to project yearly costs.
- Step 4: Read the miles per gallon (mpg), cost per mile, annual fuel cost and estimated CO2 emissions from the results.
Worked Example
After 300 miles you fill 12 gallons. The tool divides distance by fuel used to give 25 mpg. At a petrol price of $3.50 per gallon, the cost per mile is 14 cents, and for 12,000 miles a year the annual fuel bill is about $1,680. It also estimates CO2 emissions at roughly 9,400 pounds a year, using about 19.6 pounds of CO2 per gallon burned. Indian drivers can convert the result: multiply mpg by 0.43 to get kilometres per litre.
Tips and Common Mistakes
- •Tip 1: Measure over a full tank and a mix of driving conditions, because a short sample gives an unrealistically high mpg figure.
- •Tip 2: Convert for Indian conditions: one mpg equals about 0.43 km per litre, so 25 mpg is roughly 11 km per litre.
- •Tip 3: Track the result across several fill-ups to spot a sudden drop in mileage, which often signals tyre pressure or service issues.
- ✗Mistake 1: Using the tank capacity instead of the actual gallons pumped, which only matches the real figure if the tank was completely empty.
- ✗Mistake 2: Mixing up miles and kilometres, or US gallons and imperial gallons, which quietly inflates or deflates every result.
Frequently Asked Questions
How do I measure my car's real mileage in km/l?
Use the full-tank method: fill the tank completely, reset the trip meter, drive normally, then fill again and divide the kilometres driven by the litres pumped. The more fill-ups you average over, the more accurate the figure.
Why is my actual mileage lower than the ARAI figure?
ARAI mileage is measured in ideal lab conditions without traffic, AC or inclines. Real-world mileage is typically 10–20% lower, and in heavy city traffic it can be much worse — your own measured average is the number to plan fuel costs with.
Is 15 km/l good for a petrol car?
It depends on the segment: small hatchbacks typically return 15–20 km/l, sedans 12–18 km/l, and SUVs 8–14 km/l in mixed Indian conditions. Compare your result with other owners of the same model rather than a single universal number.
How much does using the AC affect mileage?
Running the AC can reduce city mileage by roughly 5–10%, since the compressor loads the engine at every stop and start. On highways the effect is smaller, often 3–5%, because the engine is already working efficiently.
What quick fixes improve fuel economy?
Keep tyres at the pressure recommended in the owner's manual — under-inflated tyres can cost 2–3% efficiency — and avoid aggressive acceleration and braking, which can cut highway mileage by 10% or more. A sudden drop across fill-ups often signals a service issue.
Compare these tools
- Money Counter Calculator — Count dollar and rupee banknotes and coins of every denomination, from $100 and ₹2000 notes down to pennies and ₹1 coins, and total cash in hand instantly
- Soup Calculator — Scale soup recipes to any number of servings and estimate the broth you need, so your pot always matches the number of people you are feeding
You might also need
Related calculators from other categories
Construction
Brick Calculator
Calculate the number of bricks, mortar volume and cost for a wall using Indian standard brick size, in feet and inches.
Health & Fitness
Caffeine Calculator
Track your daily caffeine intake from coffee, tea, energy drinks and soda. Check if you're within safe limits.
Health & Fitness
Calorie Calculator
Calculate your daily calorie needs, BMR and TDEE to maintain, lose or gain weight. Personalised for age, height, weight and activity.
Health & Fitness
Carbohydrate Calculator
Estimate your daily carbohydrate range in grams from your calorie intake, with carb targets for weight loss or muscle gain.