Gas Calculator
What Is a Gas Calculator?
A gas calculator — also called a fuel cost calculator or trip cost calculator — estimates how much you'll spend on gas for a road trip, your car's fuel efficiency in miles per gallon (MPG), or how many gallons you'll need for a given distance. These three calculations are interrelated: fuel cost = (distance ÷ MPG) × gas price per gallon.
Knowing your trip fuel cost in advance helps you budget road trips, compare the cost of driving versus flying, decide whether to fill up before a long drive, and evaluate whether a more fuel-efficient vehicle is worth the higher upfront cost.
This calculator handles all three scenarios: you provide any two of distance, MPG, and price, and it solves for the third.
How to Use This Gas Calculator
- Choose what you want to calculate: trip cost, your car's MPG, or gallons needed.
- Enter the required values (distance, MPG, gas price) for your selected mode.
- Click Calculate to see the result with a full breakdown of inputs and outputs.
- For MPG calculation, fill up your tank completely, drive until low, fill up again — use the miles driven and gallons used from the second fill-up.
Worked Example: New York to Miami Road Trip
| Input | Value |
|---|---|
| Distance | 1,280 miles |
| MPG (combined) | 28 MPG |
| Gas price | $3.50/gallon |
| Gallons needed | 45.7 gallons |
| Total fuel cost | $160 |
Add 5–10% buffer for traffic, detours, and air conditioning: budget $168–$176 for fuel on this trip.
Average MPG by Vehicle Type
| Vehicle Type | City MPG | Highway MPG | Combined MPG |
|---|---|---|---|
| Compact sedan | 28–35 | 36–45 | 32–38 |
| Midsize sedan | 24–30 | 32–38 | 27–33 |
| SUV (4-cylinder) | 22–28 | 28–35 | 24–30 |
| SUV (V6/V8) | 16–22 | 22–28 | 18–24 |
| Full-size pickup | 14–20 | 18–24 | 16–21 |
| Hybrid | 40–55 | 38–48 | 42–52 |
Tips to Improve Fuel Efficiency
- Maintain proper tire pressure: Under-inflated tires increase rolling resistance. Each PSI below optimal reduces MPG by about 0.1%.
- Reduce highway speed: Aerodynamic drag increases with the square of speed. Driving 70 mph instead of 60 mph uses 30–35% more fuel.
- Smooth acceleration: Jackrabbit starts and hard braking waste significantly more fuel than gradual acceleration and coasting.
- Avoid idling: Idling gets 0 MPG. Turn off the engine if waiting more than 60 seconds.
- Remove excess weight: Every 100 lbs of extra weight reduces MPG by about 1%. Remove roof racks when not in use.
- Use cruise control on highways: Maintains steady speed more efficiently than human foot-on-gas variation.
Frequently Asked Questions About Gas Costs
How do I calculate gas cost for a road trip?
Gas cost = (Trip miles ÷ MPG) × gas price per gallon. For a 500-mile trip in a 30 MPG car at $3.60/gallon: (500 ÷ 30) × $3.60 = $60.
How do I calculate my car's MPG?
Fill your tank completely, reset your trip odometer. Drive until nearly empty, fill up again, note how many gallons you used. MPG = miles driven ÷ gallons used.
How much does gas cost per mile?
Cost per mile = gas price ÷ MPG. At $3.50/gallon in a 28 MPG car: $3.50 ÷ 28 = $0.125 per mile (12.5 cents/mile).
How many gallons does it take to drive 1,000 miles?
Gallons = distance ÷ MPG. In a 25 MPG car: 1,000 ÷ 25 = 40 gallons. In a 35 MPG car: 1,000 ÷ 35 = 28.6 gallons.
Is it cheaper to drive or fly?
Driving is often cheaper for 1–2 passengers under 500 miles, especially factoring bag fees. Flying wins for longer trips with multiple people where you factor in lodging, meals, and time. Calculate your specific fuel cost first, then compare against flight prices.
How does AC affect gas mileage?
Air conditioning can reduce fuel efficiency by 5–25% depending on conditions. It has a larger impact at low city speeds than on the highway. At highway speeds above 50 mph, AC is more efficient than opening windows due to aerodynamic drag.
What is the average gas mileage of a car in the US?
The EPA reports the average new car fuel economy is approximately 26–28 MPG combined. The overall US vehicle fleet (including older cars) averages around 22 MPG.
How do I convert MPG to L/100km?
Divide 235.214 by MPG. 30 MPG = 235.214 ÷ 30 = 7.84 L/100km. To go the other way: MPG = 235.214 ÷ L/100km.