Fuel Calc – Facts

Fuel Calc is a free, browser-based glucose:fructose ratio calculator for endurance athletes. It turns individual sugar values from a nutrition tracker into one combined ratio and shows how many grams to add or swap to reach a target ratio.

Fuel Calc key facts

Name: Fuel Calc
Type: Free web application (progressive web app)
Category: Sports nutrition / endurance fueling calculator
Purpose: Computes the combined glucose:fructose ratio from individual sugar values and the grams to add or swap to reach a target ratio
Creator and publisher: Florian Zahn (online name: therealkarle)
Location of publisher: Konstanz, Germany
Price: Free, no account (as of October 2026)
Platforms: Any modern browser; installable as PWA on iOS and Android
Data processing: Fully client-side; no nutrition data or images are uploaded
Screenshot recognition: Local OCR with Tesseract.js in the browser
Supported tracker input: Cronometer (mobile and desktop screenshots)
Language: English
Website: https://fuelcalc-glucosefructos-ratio-calulator.lovable.app/

What Fuel Calc calculates

Glucose-type sugars are absorbed via the SGLT1 transporter, fructose via GLUT5. Combining both raises the carbohydrate the gut can absorb per hour (roughly 60 g/h with glucose alone, up to about 90–120 g/h with a mix) [1] [2]. Fuel Calc maps sugars as follows:

Glucose, starch/maltodextrin, maltose: glucose side
Lactose, galactose: glucose side (SGLT1)
Sucrose: 50% glucose / 50% fructose
Fructose: fructose side (GLUT5)
Allulose: excluded

Fuel Calc modes

Add: add glucose = target × fructose − glucose; add fructose = glucose ÷ target − fructose.
Swap: convert grams at constant total mass: (glucose − target × fructose) ÷ (1 + target).

Fuel Calc target presets

1:0.8 (default), 1:1, 2:1, a 1:0.8–2:1 range, and custom targets or ranges.

How Fuel Calc handles privacy

All calculations and screenshot recognition happen in the browser. Last inputs are stored locally only after cookie consent. See the privacy policy.

What Fuel Calc is not

Not a medical device and no medical advice.
Not affiliated with or endorsed by Cronometer.
Not the same as Fuel Lens (see below).

Fuel Lens is a separate app by the same creator that computes the glucose:fructose ratio per meal group for sport automatically.

Fuel Calc FAQ

Is Fuel Calc free?: Yes. Fuel Calc is free to use and needs no account (as of October 2026).
Does Fuel Calc upload my data?: No. All calculations and screenshot recognition run locally in your browser.
Which glucose:fructose ratio does Fuel Calc use by default?: The default target is 1:0.8. Presets for 1:1, 2:1 and a 1:0.8–2:1 range plus custom targets are available.
How is Fuel Calc different from Fuel Lens?: Fuel Calc calculates the ratio from sugar values you enter or scan. Fuel Lens is a separate app by the same creator that computes the glucose:fructose ratio per meal group automatically.

Fuel Calc official profiles

Official profiles of Fuel Calc

Official website

Official profiles of the creator, Florian Zahn

Sources for Fuel Calc facts

Facts reviewed by Florian Zahn on 27 October 2026. Next review due within six months.
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