A Free Tool · Road Trips & Commutes · Split It Fairly
How much will gas cost for your trip?
Enter the distance, your car's fuel efficiency, and the price of gas, and get the total
fuel cost, how much fuel you'll burn, and the cost per person when you split it. Works in
US units (miles, MPG, dollars per gallon) or metric (kilometers, L/100km, dollars per
liter), with a round-trip toggle. The math is exact — fuel used ×
price — so the answer is only as good as your numbers.
Total cost, fuel used & per person·US (MPG) and metric (L/100km)·Round trip & split controls
Read this first
This is a quick estimate, not a quote. The arithmetic — fuel used times the price of
gas — is exact, but the answer leans almost entirely on one input: your real-world
fuel efficiency. Speed, hills, headwinds, cold weather, a loaded car, and stop-and-go
traffic all push actual fuel use above a flat distance-divided-by-MPG figure. Use your car's
measured average rather than the window-sticker number, and treat the total as a sensible
ballpark to budget around — not a promise.
Pick your units, enter the one-way distance, your fuel efficiency, and the price of gas. Toggle round trip if you're driving back, and set how many people are splitting the cost. You'll get the total, the fuel used, and the per-person share.
One-way distance — toggle round trip below if you're returning.
Your car's real-world average beats the window-sticker figure.
One-way distance — toggle round trip below if you're returning.
Lower is better. Your dashboard usually shows this directly.
Include the driver. Set to 1 if you're covering it yourself.
Total fuel cost
Fuel used
Trip type
Cost per person
The math, honestly
How the cost is figured
It's two multiplications. First, the fuel used. In US units, gallons
burned is distance ÷ MPG — 300 miles at 30 MPG is 10 gallons.
In metric, liters burned is (distance ÷ 100) × L/100km —
500 km at 8 L/100km is 40 liters. Then the cost:
fuel used × price — 10 gallons at $3.50 is $35.00, and 40 liters
at $1.50 is $60.00.
A round trip simply doubles both the fuel used and the cost, since
you're covering the distance twice — that $35.00 one-way trip becomes $70.00. To
split the cost, divide the total by the number of people in the car:
$70.00 across four people is 70 ÷ 4 = $17.50 each.
Why the estimate drifts: the formula is exact, but real fuel use isn't
flat. Aerodynamic drag grows with the square of speed, so 75 mph burns noticeably more
than 65; hills, headwinds, a loaded car or roof box, cold starts, low tire pressure, and
stop-and-go traffic all add to it. Plug in your car's measured average, not the optimistic
sticker number, and the result lands close.
Cost of a 300-mile trip by MPG
What the same 300-mile one-way trip costs at a few common fuel-efficiency levels, with gas
at $3.50 a gallon — computed with the same distance ÷ MPG ×
price formula the calculator uses. Double the figures for a round trip.
Fuel efficiency
Gallons used300 mi ÷ MPG
One-way costat $3.50/gal
Round-trip cost× 2
15 MPG
20.00
$70.00
$140.00
20 MPG
15.00
$52.50
$105.00
25 MPG
12.00
$42.00
$84.00
30 MPG
10.00
$35.00
$70.00
40 MPG
7.50
$26.25
$52.50
50 MPG
6.00
$21.00
$42.00
A fixed 300-mile trip at $3.50/gallon, for illustration. Scale linearly for your own
distance and gas price: at twice the distance or twice the price, every figure doubles.
Enter your exact numbers in the calculator above.
Cutting the number down
The cheapest gallon is the one you don't burn. A handful of habits move real-world fuel
use more than people expect — useful when the trip cost above looks higher than you'd
like.
Ease off the highway speed
Aerodynamic drag rises with the square of speed, so the jump from 65 to 75 mph costs far more fuel than it feels like it should. Settling into a steadier, slightly slower cruise — and using cruise control on flat stretches — is the single biggest lever on a long highway trip.
Drop the roof box and dead weight
A roof box or loaded roof rack wrecks aerodynamics and can cut highway economy meaningfully even when empty. Take it off when you're not using it. Clearing heavy clutter from the trunk helps a little too, though weight matters less than drag at highway speed.
Check your tire pressure
Under-inflated tires raise rolling resistance and quietly cost you fuel for the whole trip. Set them to the pressure on the door-jamb sticker (not the max on the sidewall) when the tires are cold, and you'll recover a small but free percentage.
Smooth out the stop-and-go
Hard acceleration and late braking burn fuel and throw it away as heat. Anticipating traffic, coasting toward red lights, and accelerating gently keeps you closer to your car's best numbers. City driving is where the gap between estimate and reality opens up most.
Where to buy
Got your numbers? Here's where to pick up what you need:
The terms behind the calculator, in plain English. These are background definitions to
help you read the result, not vehicle-specific specifications.
MPG (miles per gallon)
How far your car travels on one gallon of fuel — the US measure of fuel efficiency, where higher is better. Fuel used is distance divided by MPG, so a 300-mile trip at 30 MPG burns 10 gallons. Your real-world average from the trip computer is the number to use here.
L/100km (liters per 100 kilometers)
The metric measure of fuel efficiency — how many liters it takes to drive 100 km, where lower is better. It's the inverse of MPG: it counts fuel per distance rather than distance per fuel. Fuel used is distance ÷ 100 × the L/100km figure.
Fuel used
The volume of gas the trip burns — gallons in US mode, liters in metric. It's distance divided by efficiency, and it's the quantity you multiply by the price to get the cost. For a round trip it doubles, because you cover the distance twice.
Round trip
There and back. Toggling it doubles both the fuel used and the total cost, since you're driving the one-way distance twice. If you enter the full there-and-back distance yourself, leave the round-trip toggle off so you don't double it twice.
Per-person split
The total fuel cost divided by the number of people in the car, including the driver. It's the simplest fair way to share fuel on a group trip. Some groups vary the rule — excluding the driver, or adding a little for wear — but agreeing on it before you leave avoids awkwardness at the pump.
Real-world fuel economy
What your car actually averages in your hands, as opposed to the EPA window-sticker rating measured under controlled conditions. Real-world economy is usually a bit worse, and it swings with speed, terrain, weather, and load. It's the more honest input for a trip estimate.
Frequently asked
Divide the trip distance by your car's miles per gallon to get the gallons you'll burn, then multiply by the price per gallon. For a 300-mile trip in a car that gets 30 MPG with gas at $3.50, that's 300 ÷ 30 = 10 gallons, × $3.50 = $35.00 one way, or $70.00 round trip. The calculator above does the arithmetic and splits it across passengers.
Fuel cost is fuel used times fuel price. In US units, gallons is distance ÷ MPG and total cost is gallons × price per gallon. In metric, liters is (distance ÷ 100) × L/100km and total cost is liters × price per liter. Double both figures for a round trip.
The simplest fair split is the total cost divided by everyone in the car, including the driver — a $70 round trip with four people is $17.50 each. Some groups exclude the driver since they provide the car, or add a little for wear and tear; others have the driver cover their own seat. Pick a rule before you leave so nobody's surprised at the pump. The calculator handles the even split for you.
Use your real-world average if you have it — your trip computer's lifetime or recent figure already reflects how and where you drive. The EPA window-sticker number is measured under controlled conditions and tends to be optimistic for fast highway, cold-weather, or loaded driving. If the sticker is all you've got, the highway figure is the closest match for a long trip, but expect to do a little worse.
Yes. Air conditioning puts a small but real load on the engine, and aerodynamic drag rises sharply with speed — driving 75 instead of 65 mph cuts economy noticeably because drag grows with the square of speed. A roof box, low tire pressure, hills, headwinds, and stop-and-go traffic all push real fuel use above a flat distance-÷-MPG estimate. That's why this is a starting point, not a guarantee — see cutting the number down.
The arithmetic is exact: fuel used times price is the cost. The accuracy of the answer depends on your inputs, and the biggest variable is fuel efficiency, which swings with speed, terrain, weather, load, and traffic. Use your car's measured average, round distance and gas price to what you actually expect, and treat the result as a good estimate — typically within 10 to 15 percent of what you'll really spend.
This calculator covers gasoline and diesel vehicles, where cost is fuel used times fuel price. For an electric vehicle the logic is the same in different units: energy used (kWh) is distance ÷ the car's miles per kWh, times the price per kWh. EVs usually cost less per mile to fuel — especially charging at home overnight — but it depends on local electricity rates and your charging mix. Use an EV-specific cost tool for that case.
They're inverse measures: MPG counts distance per unit of fuel (higher is better), while L/100km counts fuel per unit of distance (lower is better). The conversion is 235.215 ÷ the figure — so 30 MPG is about 7.8 L/100km, and 8 L/100km is about 29.4 MPG. This tool keeps the two modes separate, so you just enter the number your dashboard shows without converting anything by hand.
Common mistakes
Gas trip cost estimates go wrong most often at the fuel-price and MPG inputs — both are easy to misread or misapply.
Using the EPA combined rating instead of an expected highway figure
The EPA's combined MPG figure blends approximately 55% city and 45% highway driving. For a highway road trip, the relevant number is the EPA highway estimate — which is typically 10–25% higher than the combined figure. Using combined MPG on a long interstate trip understates the miles per gallon your car will actually achieve and overestimates fuel cost. EPA ratings are published at fueleconomy.gov by year, make, and model.
Entering the per-gallon price without checking which grade is at the pump
Fuel price varies by grade. If your car requires regular (87 octane) but you enter the premium (93 octane) price — which is typically $0.40–$0.70/gallon higher — the estimate will overstate your cost. Verify that the price you enter matches the grade your vehicle actually uses. Most cars specify regular; use the owner's manual or the fuel door label, not the filler cap sticker, which is sometimes wrong.
Ignoring that real-world MPG varies with load, speed, and terrain
EPA ratings are measured under standardized lab conditions. Driving at 80 mph, carrying a full load of passengers and luggage, or crossing mountain terrain can reduce actual MPG by 15–25% versus EPA estimates. For budget-critical planning, use your own fill-up data if available (miles driven ÷ gallons added), not the manufacturer's rating.