What 4ny.tools is

4ny.tools is a small collection of calculators and converters that run entirely in your browser. Each one exists because I needed it myself and the options I found were slow, cluttered, or wanted an account before they would do arithmetic. The collection is deliberately small: every tool is built, tested, and maintained by one person, and nothing is added just to have more pages.

Three rules apply to every page. Your inputs stay on your device, because the calculation runs in the browser and the server only delivers the page; the one exception is the optional share link, which stores a result only when you ask it to. The tool is usable the moment it loads, with no onboarding, sign-up, or pop-ups. And the method is visible: every calculator explains what it computes, shows a worked example, and, where the answer touches health or money, cites the studies and official guidelines behind it.

The tools, by topic

Health and fitness

The Sleep Cycle Calculator works backwards from a wake-up time, or forwards from a bedtime, in roughly 90-minute cycles so you wake between cycles rather than in the middle of deep sleep. The TDEE and Macro Calculator estimates daily energy needs with the Mifflin–St Jeor equation and splits them into protein, fat, and carbohydrate targets. The Cardiovascular Fitness Score combines resting heart rate, waist-to-height ratio, sleep, and activity into one number, with the interpretation bands explained.

Money and work

The FIRE Calculator projects when a portfolio reaches the amount needed for financial independence, and explains where the 4% rule comes from and why it is not a guarantee. The Contractor vs. Employee comparison turns a day rate into a like-for-like salary by accounting for everything a contractor has to fund out of pocket.

Everyday

The Steak Wizard gives pull and serve temperatures for each doneness and cooking method, including carryover. The Detergent Dose Calculator matches the dose to your load size and water hardness. The Clothing Size Converter maps sizes between US, EU, UK, and international standards. The Temperature Converter converts Celsius, Fahrenheit, and Kelvin with a colour cue for what the temperature feels like.

Travel and environment

The Road Trip Calculator estimates fuel cost and CO₂ for a distance and splits the cost between passengers. The Fuel Consumption Calculator converts between L/100 km, US and UK MPG, and km/L. The Carbon Footprint Calculator adds up flights, car, diet, and home energy using published emission factors.

Converters and developer utilities

The Universal Unit Converter shows every unit of a category at once, from length and mass to pressure, energy, and data. The Color Converter translates between HEX, RGB, HSL, and OKLCH; the Number Base Converter and the Text Encoder handle binary, hex, Base64, and related encodings; the Calculator respects operator precedence; and Browser & IP Info shows what your browser reveals about you.

How the calculators are built

Every tool page has the same shape: the tool first, then a short "how it works" note, then frequently asked questions. The health and finance tools additionally carry a full methodology essay with the formula, a worked example with real numbers, a limitations section that says what the tool cannot tell you, and a list of cited sources. Those pages also carry an explicit disclaimer: they are informational aids, not a substitute for a doctor, a dietitian, a tax advisor, or a financial planner. When an underlying guideline changes, the affected page is revised rather than silently rewritten.

Who runs it, and how it is funded

4ny.tools is operated under Timo Lutz Medien- und IT-Dienstleistungen, a sole proprietorship registered in Germany; the About page and the Impressum have the details. The site is funded by a small number of disclosed affiliate partnerships and contextual advertising, as described in the affiliate disclosure. No tool's output depends on either. If a result looks wrong or a source is missing, I would rather hear about it than have you quietly close the tab: the contact address is on the About page.