Guides
Short, practical explainers — each one gives you the formula, a worked example, and a free tool that does the math instantly.
How to Calculate Percentages: Formulas & Examples
The three formulas behind every percentage question, with worked examples.
BMI Explained: How to Calculate and Interpret It
What BMI is, how to calculate it, and what it can and cannot tell you.
Profit Margin vs Markup: What's the Difference?
Same profit, two very different percentages — and why it matters.
MPG vs L/100km: How to Compare Fuel Economy
Two fuel-economy scales that run in opposite directions — reconciled.
HEX, RGB and HSL: Understanding Color Codes
Three ways to write the same on-screen colour — and when to use each.
Number Bases Explained: Binary, Hex and Decimal
Why the same value is 255, 11111111 or FF — and how to convert.
How Compound Interest Works (with Examples)
Why your money grows on its own over time — and the formula behind it.
How Monthly Loan & Mortgage Payments Work
The amortization math behind every car loan and mortgage.
How Many Calories Do I Need? BMR & TDEE Explained
From resting burn to daily calories — and how to set a sensible target.
Metric vs Imperial: A Quick Conversion Guide
The handful of conversions you actually need, with quick mental tricks.
What Is Base64 and When to Use It
Turning binary into safe text — and what it is not.
How to Calculate a Tip (and Split the Bill)
Fast mental tipping and clean bill-splitting, without the awkward pause.
Small-Business Pricing: Margin, Markup, ROI & Break-Even
The four numbers behind a price that actually makes money.
Date Math: Days Between Dates, Age & Weekdays
Counting days, ages and weekdays without miscounting.
Bits & Bytes: Reading Data Sizes and Speeds
Why your 100 Mbps connection downloads at only 12.5 MB/s.
Aspect Ratios Explained (16:9, 4:3, 21:9)
What 16:9 really means — and how to resize without distortion.
How to Create a Strong Password (and Why It Matters)
Length beats symbols — and why reuse is the real danger.
What Is a QR Code and How Do You Make One?
How those little squares work — and how to make one that scans every time.
How Sales Tax & VAT Work (with Examples)
Adding tax, removing tax, and reading a receipt correctly.
How to Calculate a Discount and Sale Price
What "30% off" actually saves you, in seconds.
What Is JSON? A Beginner's Guide (With Examples)
The data format behind almost every API — explained plainly.
Word Count & Reading Time for Writers
Turn a word count into a reading time — and hit format expectations.
How to Read a JWT (JSON Web Token)
Decode a token's claims — and understand what the signature does.
Celsius to Fahrenheit: Formula & Conversion Guide
Convert either way in your head, plus the reference points worth memorising.
What Is a UUID (and When to Use One)?
The globally unique ID you can generate without a central authority.
What Is CAGR? Compound Annual Growth Rate Explained
The single yearly rate that turns any start-to-end growth into one number.
URL Encoding Explained (Percent-Encoding)
Why spaces become %20 — and when to encode.
How to Calculate Hours Worked (Timesheets & Payroll)
Turn clock times into accurate paid hours, breaks and all.
What Grade Do I Need on the Final Exam?
Exactly what you must score on the final to land your target grade.
How to Calculate Your Running Pace
Turn distance and time into a pace — and predict your finish.
How to Simplify Fractions (Step by Step)
Reduce any fraction to its simplest form, reliably.
What Is a Good Color Contrast Ratio? (WCAG)
The numbers that decide whether your text is readable by everyone.
How Much Water Should You Drink a Day?
A realistic daily target — and why it changes day to day.
How to Find the Hypotenuse (Pythagorean Theorem)
The a squared + b squared = c squared rule, and how to use it both ways.
How to Convert an Hourly Wage to an Annual Salary
Turn an hourly rate into a yearly figure — and know what actually lands.
How to Read Roman Numerals (Chart & Rules)
The seven letters and two rules behind MMXXVI.
What Is the Golden Ratio (and How to Use It)?
The 1.618 ratio, what it really is, and where the myths end.
How to Calculate Electricity Costs (kWh)
Turn watts and hours into what an appliance actually costs to run.