Calculators
Calculators work out a number from inputs you supply, and every one shows the formula it used. All 23 run in your browser, so nothing you enter is transmitted or stored.
23 tools
Everyday
- Age CalculatorCalculate an exact age in years, months and days, with total days and the next birthday.
- Date CalculatorThe date calculator measures the gap between two dates in days, weeks, months and weekdays, and shifts a date forwards or backwards by any of those units.
- Discount CalculatorThe discount calculator works out a sale price from any percentage off, and handles stacked discounts correctly, since two 20% cuts are 36% rather than 40%.
- Tip CalculatorThe tip calculator works out a gratuity at any percentage, splits the bill between any number of people, and shows what rounding up actually collects.
Maths and statistics
- Average CalculatorThis average calculator reports the mean, median, mode and range of a list of numbers, with both standard deviations, so you can see which average fits.
- Combination CalculatorThe combination calculator works out nCr and nPr side by side, with and without repetition, so the gap between a combination and a permutation is visible.
- Equation SolverThe equation solver handles ax2 + bx + c = 0, showing the discriminant, the vertex and both roots, including the complex pair when the discriminant is negative.
- Fraction CalculatorThe fraction calculator adds, subtracts, multiplies and divides fractions, simplifying the result and showing it as an improper fraction and a mixed number.
- List Sum CalculatorThe list sum calculator adds a column of numbers pasted in any format, reporting positive and negative subtotals separately alongside the count and the mean.
- Matrix Row ReducerRow-reduce a matrix to reduced row echelon form, with the rank and every elimination step shown.
- Percentage CalculatorThe percentage calculator covers five separate questions, including the difference between a change in percent and a change in percentage points, which differ.
- Ratio CalculatorThe ratio calculator simplifies a ratio of any number of parts, shows each part as a percentage of the whole, and scales the set to a new total you choose.
- Scientific CalculatorA scientific calculator with trigonometry, logarithms, powers and brackets, evaluated by a real expression parser rather than eval, so precedence is correct.
- Set Builder Notation ConverterTurn a list of numbers into set-builder notation, detecting an arithmetic pattern where one exists.
- T-Score CalculatorThe T score calculator converts a z-score or a raw value onto the mean-50, standard-deviation-10 scale used across psychometric and educational testing.
- Z-Score CalculatorThe z score calculator converts a raw value into standard deviations from the mean, and gives the matching percentile under the normal distribution curve.
Grades and study
- Final Grade CalculatorThe final grade calculator works out the score you need on the last exam to reach a target grade, and says plainly when that target is already unreachable.
- GPA CalculatorCalculate a term GPA on the 4.0 scale and roll it into a cumulative GPA with prior credits.
- Weighted Grade CalculatorCalculate a course grade from weighted components, with weights normalised automatically.
Screens and media
- Aspect Ratio CalculatorThe aspect ratio calculator simplifies a pixel ratio, scales dimensions to a new width or height, and flags any result that lands between whole pixels.
- File Size CalculatorThe file size calculator estimates video and audio file sizes from a duration and a bitrate, giving the answer in both decimal MB and binary MiB units.
- Online RulerAn online ruler drawn at life size in centimetres or inches. Calibrate it once against a bank card and the on-screen scale matches your display exactly.
- PPI CalculatorThe PPI calculator works out pixel density, dot pitch and physical screen size from a resolution and a diagonal measurement, for any display or phone panel.
What the calculators cover
The 23 calculators split into four groups. Four cover everyday arithmetic, such as a tip, a discount or an age. Twelve cover maths and statistics, from a scientific calculator and an equation solver to z-scores and matrix row reduction. Three cover grades and study. Four cover screens and media, including aspect ratio, pixel density and file size from bitrate.
Every page states the formula and defines each term in it. That is deliberate: a calculator that only returns a number leaves you unable to check whether it answered the question you meant to ask, and several of these calculations have more than one convention in common use.
Where a convention is genuinely contested, the page says which one it applies. The GPA calculator uses a 4.0 scale rather than 4.3, and the standard deviation tool reports both the sample and population figures rather than picking one.
Which calculator answers which question
Several of these overlap in subject but differ in what they take as input.
| The question | The calculator |
|---|---|
| What is the gap between two dates | Date calculator. The age calculator is built around one date and today instead |
| What percentage is this of that | Percentage calculator, which covers five separate percentage questions |
| What does this set of numbers look like | Average calculator, reporting mean, median, mode, range and both standard deviations |
| What score do I need on the final | Final grade calculator, which says plainly when a target is already unreachable |
| How large will this video file be | File size calculator, which works from bitrate rather than resolution |
| What size is this screen in pixels per inch | PPI calculator, from a resolution and a diagonal measurement |
Frequently asked questions
Do these calculators round results, and how?
Results are computed at full double precision and rounded only for display, normally to a sensible number of decimal places for the quantity. Where rounding changes the answer in a way that matters, such as a tip split between people, the page shows both the rounded figure and what the rounding collects.
Why does the age calculator disagree with another site by a day?
Because calculators differ in how they borrow days when the day-of-month subtraction goes negative. This one counts completed months, then derives years from that, which is the convention most people mean by age. A calculator that borrows a fixed 30 days will report a different figure for the same dates.
Is the standard deviation here the sample or the population figure?
Both. The average calculator reports the sample standard deviation, which divides by n minus 1, alongside the population figure, which divides by n. Statistics software usually defaults to the sample figure, and using the wrong one on a small set changes the result noticeably.
Can I rely on these for financial or academic decisions?
Treat the output as a calculation you performed rather than as advice. The arithmetic is shown on every page so you can check it, but these tools do not know your circumstances, your institution rules or your tax position. Verify anything consequential independently.