How the guides fit together
The guide library covers the same fuel-mileage calculation from three different angles: how to do it, why the math works, and when the answer is reliable enough to act on. The fuel mileage calculation guide is the central reference; the others link into it.
If you are new to fuel-economy tracking, start with the step-by-step guide and the formula math page. Those two together cover the basic case. If you manage a fleet or work in automotive engineering, the accuracy guide and the SPC guide are where the formal quality-engineering techniques (Shewhart / Western Electric rules) get applied to a fill-up log.
The guides
Foundation
How to calculate fuel mileage
The methodology in one place: the basic formula, the fill-up procedure, the worked example, and the metric-system equivalents.
Step-by-step
The step-by-step method
The fill-up protocol expanded: how to record the odometer, what to do when you can't start with a full tank, the photo-validation habit, and the worked example in full.
Mathematics
The MPG formula, with the math
The algebra, the unit-conversion constants, and the standard factor 235.214583 derived step by step. For when you need to show your work.
Accuracy
What moves the number
The factors that change your MPG result, ranked by how much each one moves the number. The point is to know which ones to control for in your use case.
Accuracy
Tightening the measurement
When you need a number you can defend (warranty, tax, fleet reporting): the protocol changes, the sources of error, and the move from a fill-up average to a process control chart.
Units
MPG, L/100km, km/L
The three global efficiency units, when each is used, the conversion formulas with the standard 235.214583 constant, and the "reciprocal trap" that catches people who assume the metrics move linearly.
Standards
EPA, WLTP, JC08
What the three global test cycles actually measure, why a US MPG sticker and a European L/100km sticker for the same car can be different numbers without either being wrong, and where JC08 stands in 2026.
Apps
Fuel tracking apps
What the popular apps (Fuelio, GasBuddy, Fuelly, Road Trip MPG, aCar) actually do, where they overlap with the calculator, and where the calculator does the same job without an account or a subscription.
Telemetry
OBD-II integration
What consumer OBD-II hardware can read from your car's computer, the limits of ECU-calculated fuel rate, and when telemetry is worth the setup.
Process control
Statistical process control for fuel tracking
Shewhart and Western Electric rules applied to a fill-up log. For fleet operators and anyone who needs to know whether a 1.5 MPG drop is signal or noise.
Where to start, by goal
I just want my MPG number
Open the calculator, enter your last two odometer readings and the gallons you added. That is your MPG for the cycle. Average three to five of these for a number you can compare to the EPA sticker.
I want to understand the math
Read the step-by-step guide for the procedure, then the math page for the algebra. The two together are the foundation.
My number is off the EPA sticker
The factors guide explains what moves the result. Real-world MPG is typically 10 to 15 percent below the EPA combined rating; the rest is either measurement noise or specific to your driving.
I'm running more than a few vehicles
Start with the SPC guide. The Shewhart / Western Electric rules are what OEM and Tier 1 supplier quality teams use, and they apply to a fill-up log the same way they apply to a manufacturing process.
How to Use This Guide Library
The guide library is organized into three skill tiers, and you can read in whatever order matches your goal. If you are brand new to fuel-economy tracking, start with the step-by-step calculation guide and the mathematics behind MPG page, those two articles together cover about 80% of what a typical driver needs. If you manage a fleet or work in automotive engineering, jump to the accuracy optimisation and statistical process control pages, which introduce the formal quality-engineering techniques used by OEMs and Tier 1 suppliers. If you are evaluating fuel-tracking apps, the 2026 app comparison reviews the leading options in detail.
Each guide is written so that it can be read independently. Where an article depends on material from a sibling article, we link forward and back explicitly so you never feel stranded mid-thought. Code samples are tested on the version of the language indicated at the time of writing; if a sample has not been verified in your exact environment, the article will tell you so and link to the relevant language documentation.
About the Author
Every guide on this site is written by Sandeep Sitoke, a fuel-efficiency specialist with a B.E. in Mechanical Engineering and 12+ years of automotive data-analysis experience. Sandeep has personally tracked more than 250,000 miles of fuel consumption across gasoline, diesel, hybrid, and battery-electric powertrains, and is the author of the methodology behind the calculator on the homepage. The full author bio and the editorial standards for this site are documented on the Why Choose Us page.
We believe in honest authorship. Every code sample in these guides is executed at least once before publication, every formula is cross-checked against a primary source (SAE International, ISO 22514, EPA, WLTP, JC08), and every measurement-error estimate is accompanied by the assumptions that went into it. If you find a mistake, please email contact@fuelmileagecalculator.com with the article URL and a citation to the correct source; substantive corrections are published in the next release cycle.
How These Guides Are Maintained
The guide library is reviewed quarterly. When a referenced standard changes, for example, when the EPA updated its 5-cycle test procedure in 2024, or when the WLTP revision 4.1 took effect in 2023, the relevant guide is updated and a date-stamped change note is added to the article. The "Last Updated" date at the top of each page tells you how current the material is. We treat technical writing as a living artifact, not a one-time publication.
If you would like to be notified when a guide is updated, the simplest way is to bookmark the article and revisit it; we do not maintain a separate email newsletter, and we do not push minor revisions through social media. Major revisions that change the recommended workflow are announced on the blog.
Frequently Asked Questions
Do I need a mechanical-engineering background to use these guides?
No. The step-by-step guide and the formula page are written for a general audience. Programming examples are introduced gently, and you can read around them if you just want the conceptual material. The statistical process control and OBD-II pages assume basic comfort with the command line and a willingness to read documentation; a mechanical-engineering background is helpful but not required.
How long does it take to work through the whole library?
The complete library is approximately 10,200 words of original content, a focused reference library. Most readers spend 1-2 hours total. The calculation pillar alone is around 2,500 words and takes about 13 minutes to read end to end.
Are the guides free?
Yes. Every guide and every calculator on this site is free to read, with no signup required. We support the site through unobtrusive advertising and through the consulting work that Sandeep does for fleet operators.
Can I reuse the code samples in my own projects?
Yes. All code snippets are released under the MIT licence unless otherwise noted in the article. The methodology, the formulas, and the worked examples are released under a Creative Commons Attribution 4.0 International (CC BY 4.0) licence. You are free to copy, modify, and ship them in commercial and open-source projects. A link back to the article is appreciated but not required.
How do I report an error or suggest an improvement?
Email contact@fuelmileagecalculator.com with the article URL and a description. We respond to substantive corrections within a week and update articles in the same release cycle that ships the fix.