Enter Your Driving Details
Your Monthly Fuel Results
Where Your Fuel Energy Goes
Speed Sweep at Your Monthly Distance
Steady highway speeds compared, using your vehicle and conditions.
| Speed | L/100 km | Monthly cost | Relative |
|---|---|---|---|
| 60 km/h | 4.65 | $89.36 | |
| 80 km/h | 6.04 | $116.05 | |
| 100 km/h | 7.83 | $150.35 | |
| 110 km/h | 8.87 | $170.37 | |
| 120 km/h | 10.01 | $192.29 | |
| 130 km/h | 11.26 | $216.11 |
Estimated Monthly Savings
Formulas Used
Understanding Fuel Cost Through Physics
Why Physics Decides Your Fuel Bill
Every drop of fuel stores chemical energy. Your engine converts only a fraction into motion. The rest leaves as waste heat.
Petrol holds about 34 megajoules per litre. Diesel holds nearer 38 megajoules. A typical engine turns roughly 20 percent into useful work.
That single number shapes your whole monthly bill. Better efficiency means fewer litres. Fewer litres mean a lower cost.
The Three Forces You Fight
Moving a car means overcoming three main forces. Aerodynamic drag grows with the cube of speed. Rolling resistance grows with vehicle weight.
Drag power is half times density times coefficient times area. Then multiply by speed cubed. Doubling speed multiplies drag power by eight.
Rolling resistance equals the coefficient times mass times gravity. Heavier cars pay more at every speed. Tyre pressure changes this force noticeably.
Stop and Go Driving Wastes Energy
Accelerating gives the car kinetic energy. Braking turns that energy into heat. A standard petrol car recovers none of it.
Kinetic energy equals half mass times speed squared. Each stop dumps that energy into your brake pads. City driving repeats this cycle constantly.
Hybrids recover part of this energy. The calculator lets you set a recovery rate. Try it to see the savings.
Fuel Energy Content Matters Too
Different fuels carry different energy per litre. Petrol holds about 34 megajoules. Diesel holds about 38, and LPG holds about 26.
A denser fuel gives more distance per litre. Price per litre alone can mislead you. Always compare cost per megajoule as well.
The calculator handles this conversion for you. Choose a fuel preset or type a custom value. Then enter your local price per litre.
How This Calculator Works
First, it finds the force needed at your cruising speed. Then it multiplies force by distance to get work. It adds braking losses from your stops.
Next, it divides by engine and drivetrain efficiency. That gives the fuel energy required. Dividing by energy density then gives litres.
Finally, it scales the result to your monthly distance. It multiplies litres by your fuel price. You also see the cost per kilometre.
Ways to Cut Your Monthly Cost
Slow down on highways first. Dropping from 120 to 100 kilometres per hour helps. Drag power falls by nearly 42 percent.
Remove roof racks and extra cargo. Keep tyres properly inflated. Smooth acceleration also reduces wasted kinetic energy.
Use the calculator to test each change. Compare scenarios before you spend money. Small physics changes add up over twelve months.
Frequently Asked Questions
How accurate is this fuel cost calculator?
It gives a solid physics estimate. Real results vary with wind, road grade, temperature, and traffic. Expect accuracy within about ten to fifteen percent for typical driving. For best results, enter honest values for speed, stops, and efficiency.
What is a good engine thermal efficiency value?
Most petrol engines reach 20 to 30 percent. Modern diesels reach about 30 to 40 percent. Hybrids can score higher. If you are unsure, use 20 percent for petrol and 33 percent for diesel.
Why does speed affect fuel use so much?
Aerodynamic drag power rises with the cube of speed. Doubling your speed makes drag power eight times larger. Drag force alone rises with the square. That is why slower highway cruising saves real money over a month.
What is the drag coefficient of a typical car?
Most cars fall between 0.25 and 0.35. Sedans sit near 0.28. SUVs and vans often reach 0.35 to 0.42. Frontal area usually ranges from 2.0 to 2.8 square metres depending on vehicle size.
What rolling resistance coefficient should I use?
Standard road tyres on asphalt sit near 0.010 to 0.015. Low rolling resistance tyres can reach 0.007. Underinflated tyres push the value higher. Use 0.012 if you are unsure.
How do stops change my fuel consumption?
Each stop wastes the kinetic energy you built up. Heavier cars waste more per stop. City routes with many stops burn far more fuel per kilometre than steady highway cruising at moderate speeds.
Does the calculator handle hybrid or regenerative braking?
Yes. Use the regenerative recovery field to enter the share of braking energy your car recovers. Standard petrol cars use zero. Many hybrids recover 30 to 60 percent of braking energy.
Can I use it for diesel or LPG vehicles?
Yes. Pick a fuel preset or enter a custom energy density. Diesel holds about 38 megajoules per litre. LPG holds about 26. Then enter your local price per litre for accurate cost results.
Does air conditioning change the result?
Air conditioning adds an accessory load, which you can enter in watts. A typical compressor draws one to three kilowatts. The calculator converts that load into extra fuel used. Set it to zero to ignore it.