Calculator tools

Everyday sums, percentages and units. 4 free tools, any file size, no account.

The sums that are easy to get subtly wrong: what a percentage of a percentage actually comes to, a grade point average across different credit weights, the spread in a set of numbers. Each one shows the figures it used, not only the answer.

Percentage of a PercentageChain two percentages from a starting value.Standard Deviation CalculatorStandard deviation, variance and mean of your numbers.Percentage CalculatorOf, is-of, change, add or take off.GPA CalculatorGrades and credits in, GPA out.

Frequently asked questions

Why not use a phone calculator?

Because the hard part is the setup, not the arithmetic. A discount on top of a discount, or a GPA across uneven credits, is where the mistake happens — these pages lay the steps out.

Is it a sample or a population standard deviation?

You choose. The tool shows both the formula it applied and the intermediate figures, so the result can be checked rather than trusted.

Do the numbers I enter go anywhere?

No. The calculation runs in the page on your device. Nothing is sent to a server and nothing is kept after you close the tab.

The same tools under other names: Percentage Change Calculator

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