E30 CalculatorEthanol blend planner
v1.0.0-beta.2

E30 Fuel Mixture Calculator

Work out exactly how many gallons of E85 and pump gas to put in to hit your target ethanol blend — for a full fill, a top-up on what's already in the tank, or to check a mix you've already pumped.

v1.0.0-beta.2 · Beta See the changelog below for what's new.
Target blend
E30 · 30%

Your two fuels

Ethanol content varies — especially pump E85. Use what's on the pump or your test-kit reading.

Pump “E85” is legally 51–83% ethanol in the US and drops in winter. If you haven't tested yours, 70–75% is a safer guess than 85%.
Most US premium (91/93) is E10. Use 0% only if you're buying ethanol-free gas.

Your tank

Presets included — or type any size.

gallons

What are you doing?

Pick the situation — the answer updates as you type.

Assumes the tank is effectively empty (or what's left is negligible). For a part-full tank, use “Top up” instead.

At the pump

Add E85 first
4.11 gal
Then top off with pump gas
10.39 gal
E85 Pump gas

Order at the pump

  1. Put the E85 in first, then fill the rest with pump gas — the gasoline going in last helps the two mix as you drive off.
  2. Round to what the pump can do. Amounts are shown to two decimals, but pumping to the nearest tenth of a gallon is plenty — a few tenths either way moves the blend by about a point.
  3. Drive gently for the first few miles while the mix evens out and, on a flex-fuel sensor or tune, the car settles on the new content.
  4. Stay in your tuner's window. An “E30” tune usually means a range around 30%, not exactly 30.00% — confirm the acceptable range with your tuner and don't chase decimal places.

Get the app — both ways

Native store apps for Windows and Android, so you can download, rate, and review it where you normally get apps. On iPhone and iPad, use the web app for now — same calculator, no download needed — until the iOS version is published officially.

Windows
Native app · Microsoft Store

For your PC

A standalone Windows app that launches in its own window — no browser tabs to hunt for. The Microsoft Store listing is the point: anyone who uses it can leave a rating and a review there.

Until the store build lands, this web version also installs from Edge or Chrome: ⋯ / ⋰ menu → Apps → Install this site as an app (wording varies by browser).

Android
Native app · Google Play

For your phone at the pump

A native Android app for Google Play, built from this same calculator — same targets, same fill / top-up / check modes, same math. Play Store ratings and reviews are built into that route.

In the meantime, open this page in Chrome and use ⋮ menu → Install app / Add to Home screen to pin it like an app.

iPhone & iPad
Web app · Available now

Use the web app today

iOS joins via the web app until the App Store version can be published officially. It runs full-screen from your Home Screen and needs no account:

  1. Open this page in Safari.
  2. Tap Share.
  3. Tap Add to Home Screen, then Add.
  4. Launch E30 Calculator from your Home Screen.

When the iOS app is published, it will move to the App Store too — with ratings and reviews there, just like the other stores.

One calculator, every platform: whichever version you use — Windows, Android, iOS web app, or this page in a browser — the blend math and results are identical. The store versions just add the store listing, ratings, and reviews on top.

Changelog

Every change and update to this app, newest first.

v1.0.0-beta.2

Current release
  • Changed — refreshed layout: a single phone-width column, a compact header with the version at the top, sentence-case headings, a stacked card flow (target, fuels, tank, mode, result), and a bottom navigation bar (Calculator · Guide · Get the app · Changelog). On wide screens the app sits centred in its column instead of stretching across the page.
  • Unchanged: every control, mode, default, and result — including the default fill of 3.87 gal E85 + 10.63 gal pump gas = 30.0%.

v1.0.0-beta.1

Pre-release history
  • Added — this changelog: a changelog inside the app and a visible version badge at the top of the page, so future updates are documented here as they ship.
  • Includes everything below from the initial build and the distribution update, in one package.

Distribution update

Pre-release history
  • Added — “Get the app — both ways” section: explains the two routes — native store apps for Windows (Microsoft Store) and Android (Google Play), where ratings and reviews live, and the web app for iPhone & iPad until an official iOS release.
  • Added — installable web app: Apple / mobile web-app support and Home Screen title (“E30 Calculator”), so iPhone users can add it from Safari via Share → Add to Home Screen and launch it full-screen.
  • Unchanged: calculator modes, defaults, and results — including the default fill below.

Initial build

Pre-release history
  • Added — the calculator: target blend slider (E10–E85) with E20 / E30 / E40 / E50 / E60 presets; adjustable E85 ethanol content (51–90%) and pump-gas content (0–15%); tank capacity with presets (Golf Alltrack 14.5 gal, Golf / GTI 13.2 gal, Focus ST 12.4 gal) or any typed size; gallons or litres.
  • Added — three modes: Fill the tank (exact E85 / pump-gas split for a fill), Top up what’s in there (accounts for fuel already in the tank and its current blend, with gauge shortcuts), and Check a mix (reports the blend you actually landed at, plus the swap that would correct it to target).
  • Added — results & guidance: “At the pump” result with amounts in both units, a blend bar, and a final-blend verdict; warnings when a target is unreachable by topping up or higher than the E85 itself; “Order at the pump” steps; and safety notes on variable pump-E85 content and only running a blend your tune is written for.
  • Default fill: 14.5 gal tank, E30 target, 85% E85 + E10 pump gas = 3.87 gal E85 + 10.63 gal pump gas, landing at 30.0%.
  • Added — light & dark appearance that follows the device setting, and a layout that stacks cleanly on phone widths.

Good to know

Pump E85 is the big variable. Its actual ethanol content swings with season and station (51–83% by US spec), which is why this calculator lets you change it. A cheap ethanol test kit — or a flex-fuel sensor / ethanol gauge if your tune supports one — takes the guesswork out.

The math is a straight volume blend: total ethanol in ÷ total fuel in. It assumes the two fuels mix evenly and ignores the tiny volume change when ethanol and gasoline combine — close enough for any pump fill.

Don't run a blend your tune isn't written for. Higher ethanol needs more fuel volume; on a stock or 93-octane tune, a strong blend can run the car lean. Only run E30 on an E30 (or flex-fuel) tune.