How Many Miles per Tank: Tank Size Times MPG

How Many Miles per Tank is one of those questions that sounds simple until you try to answer it for your own car. The number depends on the car, the journey, the weather and how you drive, so there is no single figure that fits every driver. What this page does instead is give you the method, so you can work out your own figure and know exactly what it means.

Below you will find the formula, a worked example with every step shown, a conversion table, and the factors that push the result up or down. Read the figures on this page about how many miles per tank as a worked illustration, and swap in your own miles, gallons and price to get your own answer. Fuel prices and efficiency figures used in examples are labelled as examples, because they change constantly and differ by place and by car.

The formula — how many miles per tank

MPG = miles driven ÷ gallons used. That is the point to carry into how many miles per tank: the method is the same, but the numbers are yours, so the example here is only a starting point. Everything else on this page is built on that one line. For the worked example below, the car covers 360 miles on 9.0 gallons, which gives 360 ÷ 9.0 = 40 MPG. In metric terms the same economy is 5.88 L/100km using a US gallon, or 7.06 L/100km using a UK imperial gallon — label which gallon you used, because the two figures differ by about 20 percent. The formula looks trivial, and it is, but the measurement behind it is where people go wrong: the miles must be the miles actually driven between the two fills, and the gallons must be the gallons actually pumped, not the size of the tank and not a dashboard estimate.

Worked example — how many miles per tank

Here is the calculation with the numbers filled in. The driver covers 360 miles over a week of commuting plus a weekend trip and uses 9.0 gallons, so MPG = 360 ÷ 9.0 = 40 MPG. Converted, that is 5.88 litres per 100 km on a US gallon, or 7.06 litres per 100 km on an imperial gallon. The fuel cost at an example price of $3.85 per gallon is (360 ÷ 40) × $3.85 = $34.65 for the 360 miles, or $0.10 per mile. Two checks keep this honest: first, the trip meter must have been reset at the first fill, not halfway through the tank; second, both fills must be to the same level — brim to brim is the usual standard, because stopping at the first click on one fill and brimming the next adds a phantom gallon or two. Do the same measurement over several tanks and average the totals, and the figure settles down to something you can plan around.

How far a tank takes you — how many miles per tank

Range is simply tank size × MPG, so the same car goes further on a bigger tank and further still when its MPG improves. The table shows the range for common tank sizes at the example economy of 40 MPG. Your own range is your tank size multiplied by your own measured MPG — use the dashboard's remaining-range figure only as a rough guide, because it is based on recent driving, not on the whole tank.

Tank size Range at 40 MPG
10 gallons 400 miles
12 gallons 480 miles
14 gallons 560 miles
16 gallons 640 miles
18 gallons 720 miles
20 gallons 800 miles

How to work out your own range — how many miles per tank

Your range is your tank size multiplied by your real MPG, and both halves need measuring. Find the tank capacity in the owner's manual — not the amount you can squeeze in after the pump clicks off, which varies — and multiply it by the MPG you measured brim-to-brim over several tanks. A car with a 14-gallon tank doing 40 MPG has a theoretical range of 560 miles, but treat that as a maximum: most drivers refuel well before the tank is empty, and the last gallon or two is not usable in practice. The dashboard's range estimate is a different thing again — it is based on recent driving, so it falls after a week of short cold trips and rises after a long motorway run. Use your own calculation for planning a journey, and use the dashboard only as a rough guide to when to stop.

Common mistakes — how many miles per tank

Wrong MPG figures usually come from the measurement, not the maths. That is the point to carry into how many miles per tank: the method is the same, but the numbers are yours, so the example here is only a starting point. The gallon type is the first thing to check: US and imperial gallons are different sizes, and using the wrong one moves the answer by about a fifth. The second is the fill level — brim-to-brim works only if both fills reach the same level, so stop at the first click both times or brim both times, but do not mix the two. The third is the trip meter: reset it at the first fill and read it at the second, with no reset in between. The fourth is sample size: one tank is a sample of one, and averaging three or four tanks is what turns a noisy figure into a reliable one. Get those right and the division itself is the easy part.

Related calculations — how many miles per tank

If this page answered your question, these pages take the next step — the same method applied to a closely related question, or the calculator that does the arithmetic for you. That is the point to carry into how many miles per tank: the method is the same, but the numbers are yours, so the example here is only a starting point.

Putting your how many miles per tank figure to work

Putting the figure to work is where the method pays off. That is the point to carry into how many miles per tank: the method is the same, but the numbers are yours, so the example here is only a starting point. Once you know your own MPG, measured brim-to-brim over several tanks, you can price any journey before you set off: multiply the miles by the fuel price divided by your MPG, and the answer is the fuel cost of that trip at that example price. You can also compare cars honestly, because you are comparing measured figures rather than brochure claims. Keep a simple log — date, miles, gallons, price — and review it monthly. Patterns show up quickly: a winter dip, a motorway improvement, a slow decline that points to tyre pressures or a change in routes. The log turns a vague feeling about fuel use into a number you can act on, and that is the whole point of measuring in the first place.

Using your how many miles per tank figure day to day

A useful habit is to record the figure alongside the conditions. That is the point to carry into how many miles per tank: the method is the same, but the numbers are yours, so the example here is only a starting point. Note the kind of driving each tank covered — mostly town, mostly motorway, or a mix — and the season, because both move the result enough to matter. A tank that looks disappointing after a week of short cold trips is not a problem with the car; it is a problem with the comparison. Compare motorway tanks with motorway tanks and winter with winter, and the averaged figure becomes a reliable baseline. Once you have that baseline, a genuine change stands out: a sudden drop after nothing else changed is worth a look at tyre pressures, a roof box left fitted, or a brake that is dragging. The measurement is simple; the discipline of recording it is what makes it useful.

Frequently asked questions

How do I work out how far I can drive on a full tank?

Multiply your tank size in gallons by your MPG. A 14-gallon tank at 40 MPG gives a theoretical range of 560 miles. Use your own measured MPG, not a brochure figure, and keep a reserve rather than planning to use the last miles of the tank.

Why does my dashboard range differ from my calculation?

The dashboard estimates range from recent driving, so it rises after motorway runs and falls after town driving. For how many miles per tank, the same reasoning applies — measure brim-to-brim, average several tanks, and use your own figures rather than a quoted one. Your calculation uses your averaged MPG over several tanks, which is steadier. Trust your own figure for planning and the dashboard only as a rough guide.

Should I run the tank to empty to test the range?

No. That is the point to carry into how many miles per tank: the method is the same, but the numbers are yours, so the example here is only a starting point. Running to empty risks drawing sediment into the fuel system and leaves you stranded if the estimate is optimistic. Measure range from full-tank fills and trip-meter readings instead, and plan fuel stops with a comfortable margin.

Does driving faster reduce my range?

Yes. Read the figures on this page about how many miles per tank as a worked illustration, and swap in your own miles, gallons and price to get your own answer. Aerodynamic drag rises steeply with speed, so the same tank covers fewer miles at a faster steady cruise than at a slower one. Steady driving at a moderate speed gives the best range, while stop-start traffic and high speeds both shorten it.

What size is my fuel tank?

Check the owner's manual or the manufacturer's specification for your exact model and year, rather than guessing from the amount a fill takes. Read the figures on this page about how many miles per tank as a worked illustration, and swap in your own miles, gallons and price to get your own answer. The amount pumped at a fill is not the tank size — it is the amount needed to refill what you used.