Maths & Conversion Tools
Work out a percentage, simplify a ratio, convert units or number bases, or add fractions. Every calculator shows the working, not just the answer.
Which tool do I need?
This is the quickest way to the right one.
- What is X% of Y, or what is the % change?
- Percent Calculator
- How do I simplify a ratio, or share an amount in one?
- Ratio Calculator
- How do I add or divide fractions?
- Fractions Calculator
- What is 0.375 as a fraction?
- Decimal to Fraction
- How many kilometres is a mile?
- Unit Converter
- What is this number in binary or hex?
- Base Converter
- What is this colour as a hex code?
- Hex ↔ RGB Converter
- What are the odds of this happening?
- Probability Calculator
Maths guides
Longer explanations of the formulas behind the tools.
Quick Maths Reference
Number bases
Decimal (base 10) is the everyday number system. Binary (base 2) uses only 0 and 1 and underpins all digital computing. Hexadecimal (base 16) uses digits 0–9 plus A–F and is used for memory addresses and colour codes. Octal (base 8) appears in Unix file permissions. Converting between them is arithmetic, not magic.
Working with fractions
To add or subtract fractions, find a common denominator first. To multiply, multiply numerators and denominators directly. To divide, flip the second fraction and multiply. Always simplify the result by dividing both numerator and denominator by their greatest common divisor (GCD). The result should be in lowest terms.
Percentages in practice
Three types of percentage problem arise most often: finding a percentage of a number, finding what percentage one number is of another, and calculating percentage change. Percentage change = (new − old) ÷ old × 100. A negative result is a decrease; positive is an increase. Percentage point change is a simple difference, not a ratio.
Probability basics
Probability ranges from 0 (impossible) to 1 (certain). For independent events — where the outcome of one does not affect the other — the probability that both occur is their individual probabilities multiplied together. The probability that at least one occurs is 1 minus the probability that neither occurs.
Maths calculator questions
- What is the difference between percentage change and percentage points?
- A rise from 20% to 25% is a five percentage point increase, but a 25% increase in percentage terms. Both are correct and they mean different things, which is why the same figure is often reported two ways. The Percent Calculator gives both.
- Why does a ratio simplify differently from a fraction?
- They are the same arithmetic used for different questions. 3 : 5 is part to part — three of one thing for every five of another. As a fraction of the whole, that first part is 3/8, not 3/5. Mixing the two up is the single most common ratio mistake, so the Ratio Calculator prints both.
- Are the unit conversions exact?
- Where the definition is exact, yes: an inch is exactly 25.4 mm, and a mile is exactly 1609.344 m, so those conversions are exact by definition rather than measured. Results are rounded for display, and each tool states the precision it shows.
- Do these show the working?
- Yes. Each calculator prints the formula it used and the same formula with your numbers substituted in, so the result can be checked by hand rather than taken on trust.