What Is a Hash Function? (MD5, SHA-256)
A hash function turns any input into a fixed-size fingerprint. Here's what it does, its key properties, common uses, and which algorithms are safe.
Daniel Okonkwo · 2 min read
Guides & tutorials
Practical guides, how-tos and comparisons to get the most out of our free online tools.
October 2, 2025
October 1, 2025
How to Find a Cube Root by Hand
A step-by-step guide to finding a cube root by estimation and refinement — plus how it differs from a square root and when a value stays irrational.
Lena Hoffmann · 3 min read
Simple vs Compound Interest: What's the Difference?
Simple interest grows in a straight line; compound interest snowballs. Here's how each works, a worked example, and which one you meet in real life.
Camille Laurent · 2 min read
September 30, 2025
What Is a Factorial? n! Explained Simply
A factorial multiplies every whole number down to 1. Learn what n! means, how fast it grows, and why it powers permutations and combinations.
Lena Hoffmann · 3 min read
How Many Calories Do You Burn a Day?
Most adults burn 1,600–2,400 a day, mostly just staying alive. Here's the three parts of daily burn, typical totals, and how to estimate yours.
Sofia Nunes · 2 min read
September 29, 2025
Emoji Are Harder Than They Look: Why "Just Strip the Emoji" Has No One-Line Answer
One visible emoji can be one code point or fourteen UTF-16 units. We ran three popular regexes against a real sentence and each broke differently — one deleted the digits. Here is why, which Unicode property answers which question, and the grapheme-cluster rule that actually works.
Daniel Okonkwo · 13 min read
September 26, 2025
The Fake Fonts in Your Bio Are Not Fonts: What Those Characters Really Are
A bold-looking 𝐀 is not the letter A in a bold font — it is U+1D400, a separate character invented for mathematics. We printed the code points, measured what it costs in bytes, broke search, sorting and word counts with it, and scanned the block to find its 28 holes.
Daniel Okonkwo · 13 min read
What Grade Do You Need on Your Final?
Work out the exact final-exam grade you need to hit your target, from your current grade and the exam's weight. Here's the formula and an example.
Lena Hoffmann · 3 min read
September 25, 2025
Markdown: A Beginner's Guide
Format plain text with a few symbols: # for headings, ** for bold, - for lists. Here's what markdown is, the core syntax, why it's everywhere, and the gotchas.
Daniel Okonkwo · 3 min read
The Pythagorean Theorem Explained
In a right triangle, a² + b² = c². Here's what the formula means, a worked example, how to find any side, and where it's used in real life.
Lena Hoffmann · 2 min read
September 24, 2025
How Much Concrete Do You Need?
Concrete is measured by volume: length × width × depth. Here's how to work out cubic metres, add for waste, and choose bags or ready-mix.
Marco Bianchi · 3 min read
September 23, 2025
LCM and GCD Explained
The GCD is the biggest shared divisor; the LCM is the smallest shared multiple. Here's what each means, how to find them with prime factors, and the shortcut linking them.
Lena Hoffmann · 3 min read