I'm trying to convert my gas mileage from kilometers to miles and litres to gallons. I drove 437.4 kilometers and used 38.017 litres. What is my miles per gallon? Canadian

You could try the old fashioned way of checking your mileage. Start with a full tank of fuel. Make a note of the total mileage on the vehicle. Drive the vehicle normally normally until the low fuel light comes on. Refill the tank to full and write down how many litres/gallons you put in. Next check your total mileage display again and write that down as well. From those numbers you can work out you fuel consumption.
Subtract you first mileage number from the current mileage number to get your total miles driven. Then it's Miles driven divided by gallons of fuel used.
As most European pumps measure in litres you'll need to divide the total litres you used by the number of litres to the gallon. Then you can divide the mileage done by that number.
*Note* The American gallon is smaller than the UK 'Imperial' gallon so make sure you use the correct one.
[ UK = 4.55 litres to the gallon (Imperial)].
[ USA = 3.78 litres to the gallon].

as lpg expands to around 200 times the liquid state it will be difficult to calculate as how you want it
the car has a liquid tank but the liquid is converted to gas in a converter on the manifold.
basically from experience an engine on lpg gets about 75% of the mileage as if it was on petrol for the same amount of lpg in litres
talk wit an accredited specialist automotive gas fitting shop and they may be able to give you a better idea
you can work it out by filling the lpg tank to shut off and setting the trip meter to zero and then when you have done say 100 klms refill the lpg tank to shut off and that will indicate how many litres were used in that 100 kilometers

do you want to figure out how to figure yours out. a 20 year old car nothing is going to be average. to get it better lose some weight in the car. meaning don't carry 500 lbs of stuff you don't need. the less it weights the less the engine has to work which saves gas use. fill your tank normal till the pump shuts off and don't pull the handle to add more fuel. then write down the mileage. drive the car 200 miles. fill the tank again the same way. then figure out the miles you drove and how much gas you put in the tank. if you drove 200 miles and used 10 gallons you get 20 miles to the gallon. doing a tune up and checking your air in the tires can increase the mileage. good idea to check it first before doing the tune up to show it did some good. I did a tune up once and got almost 5 more miles to the gallon after

462.6 km is about 287.4 miles. 33.17 liters is about 8.76 gallons. Dividing 287.4 miles by 8.76 gallons gives about 32.8 miles per gallon.

First, are we talking about a Nissan or a Toyota? (You posted your question in the Toyota section).
Second, your mileage works out to 7 miles per US gallon (sorry, I can't think in liters and kilometers). SOMETHING IS LEAKING, because there's no way a modern engine could use that much fuel if it was running in normal or semi-normal fashion.
What were the "few things changed?" I suspect a leaking fuel hose or connection.

to see what you get for mileage, take it to a gas station and fill it till the pump stops and reset your trip meter. Drive it around like you normally would to work or whatever till the tank is almost empty and go fill it up again till the pump stops. Its best to go to the same pump you used before. Once it is full look to see how many gallons or liters you put in(This is how many you used since the last time you filled up). Take the number of miles/kilometers from your trip meter(the number of miles/kilometers you drove since you last filled up) and divide it by the gallons/liters you used and you will get your miles/kilometers per gallon/liter. Compare this with the rating your vehicle is suppose to get. But remember it can very depending on how you drive.
Miles/kilometers divided by gallons/liters

Fuel Info Fuel Tank Capacity: 23 Gallons. EPA Mileage Estimates: (City/Highway/Combined) Automatic: 13 mpg / 19 mpg / 15 mpg Range in Miles: Automatic: 299 mi. / 437 mi. / 345 mi.

push in on the little mileage reset knob and hold it in for a couple seconds.  Works on cars other than Renault ... hopefully there too.