Gas Mileage Calculator Ontario: MPG & L/100km

This gas mileage calculator works out your fuel consumption in the units Ontario drivers actually see at the pump: litres per 100 kilometres (L/100 km) and kilometres per litre (km/L), plus the US-style miles per gallon (MPG) if you need it. You enter the distance you travelled and the fuel you used to cover it, and the calculator returns your average fuel economy, which is the number you compare against your car’s official rating or use to estimate your next fuel bill.

Formula

The core formula for fuel consumption in litres per 100 kilometres is:

Fuel consumption (L/100km) = (Fuel used in litres ÷ Distance travelled in kilometres) × 100

Where:

• Fuel used (f) – the amount of fuel your vehicle burned, measured in litres (L). This is the total fuel you put in to refill the tank, assuming you started and ended with the same tank level.
• Distance travelled (d) – the distance you drove during that same period, measured in kilometres (km). This comes from your trip odometer or the difference between two full-tank odometer readings.
• Fuel consumption (fc) – the result, expressed in litres per 100 kilometres (L/100 km). Lower numbers mean better fuel economy.

The two secondary outputs are simple rearrangements: kilometres per litre is distance divided by fuel (d ÷ f), and miles per gallon is the same ratio converted to imperial units. The calculator uses the US gallon (3.785 litres), which is the standard for MPG figures in North American car specifications.

Worked Example

Using the default values from the calculator above – a 400 km trip and 40 litres of fuel used – the calculation works like this:

1. Divide the fuel used by the distance: 40 L ÷ 400 km = 0.1 L per km.
2. Multiply by 100 to get litres per 100 km: 0.1 × 100 = 10.00 L/100km.
3. For km/L: 400 km ÷ 40 L = 10.00 km/L.
4. For MPG (US): first convert distance to miles (400 ÷ 1.609344 = 248.55 miles) and fuel to US gallons (40 ÷ 3.785411784 = 10.57 gallons). Then 248.55 ÷ 10.57 = 23.52 mpg.

So the default trip gives a fuel consumption of 10.0 L/100km, which is typical for a mid-size SUV or an older compact car in mixed driving. The calculator rounds each output to two decimal places, which is precise enough for comparing trips or estimating costs.

Why Ontario Uses L/100km

Canada adopted the metric system for fuel economy labelling in the 1970s, and today every new car sold in Ontario displays its official fuel consumption rating in litres per 100 kilometres on the EnerGuide label. The L/100km format is sometimes confusing because lower numbers are better – a car that uses 6.0 L/100km is more efficient than one that uses 9.0 L/100km. This is the opposite of MPG, where higher numbers are better. Ontario drivers also see kilometres per litre on some dashboards and in fleet reports, but the official standard remains L/100km. When you hear someone say “my car gets 8 litres per hundred,� they are quoting the same figure this calculator produces.

How to Measure Your Own Fuel Economy

To get an accurate reading, you need a consistent method. The most reliable approach is the full-tank method:

1. Fill your tank completely and reset your trip odometer to zero. Note the current odometer reading if your car lacks a trip meter.
2. Drive normally until you need fuel again – the longer the distance, the more accurate the result. A single short trip can be skewed by traffic, idling, or a slightly different fill level.
3. Fill the tank completely again, using the same pump and the same “click off� point if possible. Write down the litres shown on the pump.
4. Read the trip odometer (or subtract the two odometer readings) to get the distance in kilometres.
5. Enter those two numbers into the calculator above.

Repeat this over three or four tankfuls and average the results to smooth out variations from highway versus city driving, weather, and traffic. A single tank might show 9.5 L/100km one week and 11.2 the next; the average over a month is far more meaningful.

Common Mistakes and Misconceptions

The biggest error people make is mixing units. If your trip odometer reads in miles (on an imported US vehicle) or you fill up in US gallons (near the border at a US station), the numbers will be wrong. Always convert to kilometres and litres first. Another frequent mistake is not filling the tank to the same level each time – if you start with a half tank and end with a full tank, the fuel used does not match the distance driven. The calculator assumes you started and ended at the same fill level, so partial fills invalidate the result.

A common misconception is that the car’s dashboard display is accurate. Many vehicles show an “average fuel economy� figure that can be optimistic by 5–10% compared to a hand calculation. The dashboard uses engine computer data and often does not account for fuel burned while idling or during short trips. The manual calculation from this calculator is the ground truth.

Another misconception is that L/100km and km/L are the same thing. They are reciprocals – a car that does 10 km/L uses 10 L/100km. To convert between them, divide 100 by the number you have. For example, 8 L/100km equals 100 ÷ 8 = 12.5 km/L. The calculator gives you both so you do not have to do the mental math.

How to Use the Result

Once you have your fuel consumption figure, you can use it in several practical ways:

• Compare against the official rating: Your real-world number will usually be higher (worse) than the EnerGuide city or highway rating because those tests are done in controlled conditions. A 10–20% difference is normal.
• Estimate fuel costs: Multiply your L/100km by the distance you plan to drive, divide by 100, then multiply by the current fuel price per litre. For example, a 500 km trip at 8.5 L/100km uses 42.5 litres. At $1.50/L, that is $63.75.
• Track changes over time: A sudden increase in fuel consumption (say, from 9.0 to 11.0 L/100km) can signal a maintenance issue – underinflated tires, a dirty air filter, or a faulty oxygen sensor. Gradual increases often come from winter fuel blends, cold starts, or carrying extra weight.
• Plan a budget: If you commute 60 km per day and your car uses 8.0 L/100km, you burn about 4.8 litres per day. Over a 22-day work month, that is roughly 106 litres – a number you can plug into your monthly expenses.

Limits of the Formula

This calculator gives you the average fuel consumption over the distance and fuel you entered. It does not account for driving conditions, traffic, load, tire pressure, or weather – all of which can change your real-world number by several L/100km. It also assumes the fuel you put in is exactly what was burned, which is only true if you started and ended with the same tank level. For a single trip, the result can be noisy; for a monthly average, it is quite reliable. The formula is the same one used by every fuel economy tracking app and by government test procedures, so the math is not the source of error – the measurement is.

Frequently Asked Questions

What is a good gas mileage in Ontario?

For a typical compact car, 6.5–7.5 L/100km on the highway and 8.0–9.5 L/100km in the city is considered good. SUVs and trucks usually run 9.0–13.0 L/100km. Hybrids can go below 5.0 L/100km, and pure electric vehicles use no liquid fuel at all. Compare your number to the official EnerGuide rating for your specific model rather than a generic “good� value.

How do I convert L/100km to MPG?

Divide 235.21 by your L/100km figure to get US MPG. For example, 8.0 L/100km equals 235.21 ÷ 8.0 = 29.4 mpg. To go the other way, divide 235.21 by the MPG. This calculator does the conversion for you, but the constant works because 1 US gallon equals 3.785 litres and 1 mile equals 1.609 kilometres.

Why is my car using more gas in winter?

Winter fuel blends have slightly less energy per litre, cold engines run richer until they warm up, and idling to defrost or warm the cabin burns fuel without moving the car. Tire pressure drops in cold weather, increasing rolling resistance. Together, these can raise fuel consumption by 10–20% compared to summer driving. It is normal and not a sign of a mechanical problem.

Can I use this calculator for a single trip?

Yes, but the result will be less accurate than a full-tank average. A single trip includes cold starts, traffic lights, and short distances where the engine is less efficient. For a meaningful number, drive at least 100 km and combine several trips. The calculator works for any distance, but the longer the distance, the more representative the result.

Does the calculator include the cost of gas?

No. It only computes fuel consumption in L/100km, km/L, and MPG. To get a cost estimate, take your L/100km result, multiply by the distance, divide by 100, and multiply by the current price per litre at your local station. Prices vary widely across Ontario, so the calculator leaves that step to you.

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in d | Distance | km | 400 | 0
in f | Fuel used | L | 40 | 0
out fc | Fuel consumption | L/100km | f / (d / 100) | 2
out kl | Kilometres per litre | km/L | d / f | 2
out mpg | Miles per gallon (US) | mpg | (d / 1.609344) / (f / 3.785411784) | 2