How accurate is the car's 'distance to empty'?

It's a moving estimate from recent consumption, so it shifts as your driving changes and gets less reliable near empty. Use it as a guide, not a promise, and refuel with margin to spare.

How do I convert between mpg and L/100 km?

They're inversely related: L/100 km = 235.2 ÷ mpg (US). So 30 US mpg ≈ 7.8 L/100 km. Note a UK gallon differs from a US gallon, so check which mpg a figure uses.

Why does my range drop faster on the highway?

Aerodynamic drag grows sharply with speed, so a petrol or diesel car often uses more fuel per mile at 75 mph than at 55 mph. Steady, moderate speeds stretch the fuel you have.

Does this work for a diesel too?

Yes. The method is identical for petrol and diesel — just use that engine's real economy. Diesels are often more efficient, so the same fuel goes a bit further.

How Far Can I Drive on the Fuel I Have Left?

Published 2/6/2026 · 3 min read · Car calculators

Marco Bianchi — Home, DIY & motoring writer at Allin

Renovation · Materials

Checked against 2 sources

View profile →

In short

Multiply the fuel you have left by your car's fuel economy. With 4 gallons left and a car doing 30 mpg, that's about 120 miles — but keep a safety margin and don't run the tank dry. In metric terms, if you have 15 litres and the car uses 6.5 L/100 km, range = 15 ÷ 6.5 × 100 ≈ 230 km. Your dashboard 'distance to empty' does the same maths from recent driving.

A car speedometer with the low-fuel warning light lit. — John Joshua Mejia Jose · Pexels · Pexels

Estimate remaining range from fuel left and your car's economy. A simple method for gas and diesel, with a worked example and a safety margin.

Fuel left times economy

Range from remaining fuel is a one-line calculation. In US units, multiply gallons left by miles per gallon: 4 gallons at 30 mpg is about 120 miles. In metric, divide litres by consumption per 100 km and multiply by 100: 15 litres at 6.5 L/100 km is about 230 km. Both are the same idea — energy on board divided by how fast you use it.

Real economy beats the brochure

Use your own measured economy, not the manufacturer's best-case figure. City driving, cold starts, a loaded car, roof boxes and high speeds all worsen it. The most reliable number comes from filling up, resetting the trip meter, and dividing distance by fuel used at the next fill. Then keep a margin on top.

Never trust the last drops

Keep a buffer of at least 10-15%. Fuel gauges are non-linear near empty, the reserve is smaller than it looks, and running completely dry can suck debris into the fuel system and damage the pump. Treat the low-fuel light as 'refuel soon', not 'keep going until it stops'.

Worked with our own calculator

Fuel range calculator

Given

Tank size (L): 45
Consumption (L/100 km): 3.3

Result

Range (km): 1,364

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

How accurate is the car's 'distance to empty'?: It's a moving estimate from recent consumption, so it shifts as your driving changes and gets less reliable near empty. Use it as a guide, not a promise, and refuel with margin to spare.
How do I convert between mpg and L/100 km?: They're inversely related: L/100 km = 235.2 ÷ mpg (US). So 30 US mpg ≈ 7.8 L/100 km. Note a UK gallon differs from a US gallon, so check which mpg a figure uses.
Why does my range drop faster on the highway?: Aerodynamic drag grows sharply with speed, so a petrol or diesel car often uses more fuel per mile at 75 mph than at 55 mph. Steady, moderate speeds stretch the fuel you have.
Does this work for a diesel too?: Yes. The method is identical for petrol and diesel — just use that engine's real economy. Diesels are often more efficient, so the same fuel goes a bit further.

Articles you may find interesting

All guides →

How-toHow Long Does It Take to Charge an EV?Charging time is battery energy needed divided by charger power. See how home AC and public DC compare, and why fast charging slows past 80%.ExplainerWhat Affects an Electric Car's Range?Battery size, efficiency, speed, cold weather and terrain all move an EV's real range far from the sticker figure. Here's how each factor works.ExplainerYour Flight's Carbon Footprint, ExplainedHow much CO₂ does a flight emit? Learn the per-passenger-kilometre figures, why short hops are worst per mile, and what the numbers really mean.How-toSpeed, Distance and Time: The Formula and How to Rearrange ItOne triangle, three formulas. Learn speed = distance / time, rearrange it for distance or time, and keep your units consistent so the answer is right.How-toHow to Improve Fuel Economy: Driving Habits That Actually SaveSmoother driving, correct tire pressure, less weight and lower motorway speed can cut fuel use noticeably. Here is what each one is worth.How-toHow to Estimate Flight Time: Distance, Cruise Speed and OverheadEstimate a flight's duration by dividing the great-circle distance by cruise speed, then adding taxi, climb and descent overhead. A simple, reliable method.

Sources

Spotted a mistake in this article?