Breakeven point: How many Km a day justifies CNG or LPG conversion

Petrol is expensive. Diesel is rising too, so the next best option is to convert your petrol car to run on CNG or LPG. But how many kilometres a day of running justifies this conversion cost? When will you make up that investment in a gas-driven car?

CarToq works out the economics of converting your petrol car to LPG or CNG and tells you when you will recover your investment.

For instance, if you own a mid-size petrol sedan like a Honda City, and it gives an average of 12 kmpl in the city, running it on petrol would work out to a running cost of Rs. 5.70 per kilometre. If your daily running is about 50 km per day, it would cost you Rs. 285.25 daily. Assuming you use the car for 25 days a month, that’s Rs. 7,131 per month running cost on petrol.

Now let’s look at how the other alternate fuels would help save costs and when you can make up your investment in the conversion kits.

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Running on CNG


For a car like the Honda City, a good CNG conversion kit will cost at least Rs. 50,000 for a sequential kit. This includes a 14 Kg cylinder. A full tank of CNG, however, won’t hold 14 Kg (as that’s at peak pressure) and usually tops of at about 10 Kg. Larger cars with good sequential kits and a 14 Kg tank usually get a range of up to 150 km in the city, translating to mileage of about 15 kmpl. Assuming the City running on CNG gives you 15 kmpl, here’s how your running costs now work out.

The per KM running cost of the City now comes down to Rs. 2.55 per KM. For a 50 km trip daily, it would cost you about Rs. 127.80. If you use the car 25 days a month, it comes to Rs. 3,196 per month, running on CNG.


Running on LPG


LPG is not as fuel efficient as CNG or petrol and usually gives a slightly lower mileage. But the conversion costs to LPG are lower. A good kit for the Honda City would cost about Rs. 25,000 on average. Cylinder sizes are smaller than CNG, but have similar capacity. The advantage is that it saves on boot space, in case you want to carry luggage. However, fuel efficiency would drop to about 11 kmpl on LPG. Here’s how the running costs now work out.

The per KM running cost of the Honda City running on LPG would work out to Rs. 3.88 per kilometre. For a 50 Km daily run, it would cost you Rs. 194 per day. For a 25-day working month, the car would cost Rs. 4,850 to run.

Now let’s take a look at how many KM do you need to actually run your car for you to justify the additional investment in converting it to CNG or LPG.


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Breakeven point

First let’s take CNG. The cost of converting it is Rs. 50,000. Add that to the daily running cost. To get your payback period divide the cost of this kit, but the difference between the per km running cost on petrol and CNG. You will need to drive the car 15,873 km before you begin to save substantially by running on CNG.  If the car runs 50 km a day, this would take just 318 days! Or less than a year to begin saving on fuel costs.

If you convert the car to LPG, the breakeven is sooner because of the lower cost of conversion. The car will need to run only 13736 Km before you begin saving on fuel costs. If the car runs 50 km a day, you will begin to recover all your investment on LPG after 275 days or running or in the 9th month of ownership.

If your car runs more than 50 km a day, your payback period would be sooner. If it runs 100 km a day, you will recover your investment within five months for CNG and about four months for LPG!