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Practical guides for real tasks — written by the people building the tools on this site.
Showing 2,332–2,352 of 2,474 articles
🩺 Health & Fitness
How to Calculate Body Surface Area for Dosing
Calculate body surface area (BSA) from height and weight using the Du Bois, Mosteller, or Haycock formula, right in your browser, for dosing or clinical reference.
🔒 Security & Privacy
How to Calculate a Password's Entropy in Bits
Calculate a password's entropy in bits and an estimated offline crack time based on its real character set and length, not just a vague colored strength meter.
🧮 Math & Science
How to Calculate Permutations and Combinations
Calculate nPr permutations and nCr combinations from n and r with exact, arbitrary-precision results, right in your browser, for homework or probability work.
📉 Math & Science
How to Calculate Variance and Standard Deviation
Calculate mean, sample or population variance, and standard deviation from a pasted list of numbers, right in your browser, without a spreadsheet or manual formula.
📈 Finance Calculators
How to Calculate Your Annualized Investment Return
Calculate total gain and annualized XIRR return from multiple dated contributions, withdrawals, and a current value, right in your browser, no spreadsheet formula needed.
📏 Health & Fitness
How to Calculate Your Waist-to-Hip Ratio
Calculate your waist-to-hip ratio and WHO risk category from waist and hip measurements, right in your browser, without manually applying the WHO formula.
🎙️ Video & Audio
How to Change Your Voice Online for Free
Record a clip with your microphone and apply a robot, chipmunk, or echo effect in your browser, without installing voice-changing software or a Discord plugin.
📡 Network
How to Check a Server's Ping and Latency Online
Test round-trip time, packet loss, and latency to any website or server from your browser, without installing a desktop ping tool or opening a terminal.
🔍 PDF Tools
How to Check If a PDF Has a Real Text Layer
Check whether a PDF already has selectable, searchable text or is just a scanned image, page by page, before you rely on copy-paste or search working.
🔌 Network
How to Check If a Port Is Open on Your Server
Understand what an open TCP port actually means, why browsers can't check one directly, and how to think about port checking before you deploy a service.
📧 Text & Writing
How to Check if an Email Address Is Actually Valid
Validate an email address's syntax instantly, one address or a pasted list, and see the exact plain-language reason anything invalid fails before you send.
🎨 Design & Color
How to Check WCAG Color Contrast for Free
Check the contrast ratio between text and background colors for WCAG AA/AAA compliance, with live pass/fail results, before shipping a design that fails an audit.
💻 Developer Tools
How to Choose an Open-Source License for Your Project
Get a suggested open-source license — MIT, Apache 2.0, MPL-2.0, GPLv3, or PolyForm Noncommercial — from three quick questions, right in your browser.
💰 Finance Calculators
How to Compare Roth vs Traditional Retirement Accounts
Compare the after-tax future value of Roth and Traditional retirement contributions based on your tax rates and expected return, right in your browser.
🎬 Video & Audio
How to Compress a Video Without Losing Quality
Shrink a video's file size in your browser using FFmpeg compiled to WebAssembly, so it fits an upload limit or email attachment without visible quality loss.
🌙 Design & Color
How to Turn a Light CSS Palette Into Dark Mode
Convert a light-theme CSS color palette into a working dark mode by inverting lightness while keeping hue and saturation, without redesigning every color by hand.
📚 PDF Tools
How to Convert a PDF Into an FB2 eBook File
Convert a text-based PDF into a valid FB2 FictionBook e-book file with custom title and author, so it opens properly in FB2-compatible e-readers.
🖼️ Image
How to Convert a Photo Into a Vector SVG
Turn a raster photo into a scalable, posterized SVG using adjustable color and detail levels, entirely in your browser with no software install.
🩸 Health & Fitness
How to Convert A1C to Average Blood Glucose
Turn an A1C percentage into estimated average glucose (eAG) in mg/dL or mmol/L using the ADAG study formula, and see what the number does and doesn't tell you.
📖 PDF Tools
How to Convert an EPUB eBook Into a PDF
Convert an EPUB file's chapter text into a plain, paginated PDF by reflowing the text, so you can read or print it anywhere a PDF works but EPUB doesn't.
🎧 Video & Audio
How to Convert Audio Between MP3, WAV, and FLAC
Convert audio files between MP3, WAV, OGG, FLAC, and M4A in your browser when an app rejects a format, without installing desktop audio conversion software.