Standard Deviation Calculator
Calculate standard deviation, variance, and mean.
📊 Uses population standard deviation (÷N). For sample stddev, multiply by √(N/(N−1)).
What Is This Tool?
Standard deviationmeasures how spread out a set of numbers is from the average. A small standard deviation means values cluster tightly around the mean; a large one means they're widely scattered. This is one of the most useful statistics in data analysis.
What Standard Deviation Tells You
If test scores have a mean of 75 with a standard deviation of 5, most scores fall between 70 and 80. With the same mean but a standard deviation of 15, scores spread from 60 to 90. Same average — very different picture.
The 68-95-99.7 Rule
For normally distributed data: ~68% of values fall within 1 standard deviation of the mean, ~95% within 2, and ~99.7% within 3. So if adult heights average 170 cm with SD 7, about 95% of people are between 156 and 184 cm.
Population vs. Sample
This calculator uses population standard deviation (divides by N). If your data is a sample from a larger population, use sample standard deviation (divides by N−1) to get an unbiased estimate. Multiply our result by √(N/(N−1)) to convert.
Frequently Asked Questions
When do I use population vs. sample?
Use population when your data is the entire group of interest (all students in a class). Use sample when your data represents a larger population (100 voters surveyed to estimate a country).
About the Standard Deviation Calculator
The Standard Deviation Calculator lets you figure out standard deviation calculatorinstantly, without reaching for a spreadsheet or doing the math by hand. Whether you're planning a budget, checking a loan, or working through homework, the tool applies the correct formula behind the scenes and shows the result the moment you enter your numbers.
Unlike a static chart or table, this calculator adapts to your exact inputs. You can adjust any value and see the outcome update in real time, which makes it easy to compare scenarios — for example, "what if the rate were 1% lower?" or "what if I paid an extra $50 a month?"
How to Use This Tool
- Enter the main values the calculator asks for (for example, amount, rate, and time).
- Pick the right unit or option where the tool offers a choice.
- Read the result, which appears instantly below the inputs.
- Adjust any field to test a different scenario — the answer updates without a reload.
- Copy or note the result. Nothing is stored, so close the tab when you're done.
Why Use an Online Calculator?
Browser-based tools like this one have a few real advantages over installed software or manual methods:
- No installation. It opens instantly in any browser, on any operating system.
- Private by default. Everything runs locally, so your data stays on your device.
- Always up to date.There's nothing to update — you always get the latest version when you load the page.
- Free and unlimited. Use it as often as you like, with no account and no caps.
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