Z-Score Reference
| Z-Score | Percentile | Data within |
|---|---|---|
| ±1.0 | 16th / 84th | 68.3% |
| ±1.645 | 5th / 95th | 90% |
| ±1.96 | 2.5th / 97.5th | 95% |
| ±2.0 | 2.3rd / 97.7th | 95.4% |
| ±2.576 | 0.5th / 99.5th | 99% |
| ±3.0 | 0.13th / 99.87th | 99.7% |
Z-Score Calculator
Calculate the z-score (standard score) for any data point. Find the percentile rank and probability from a z-score, or calculate a z-score from a raw value, population mean, and standard deviation.
Standard Score Calculator
Frequently Asked Questions
What does a z-score tell you?
A z-score tells you how many standard deviations a data point is from the mean. A z-score of 0 means exactly average. A z-score of +2 means 2 standard deviations above average (about the 97.7th percentile). A z-score of −1 means 1 standard deviation below average (about the 16th percentile).
What is a good z-score for a test?
It depends on context. In a normal distribution, z-scores above +1 are in the top 16%, above +2 in the top 2.3%. For standardized tests, schools often look at z-scores above +1.5 to +2 as strong performance. For quality control, z-scores beyond ±3 are considered outliers (less than 0.3% of data).
About the Z Score Calculator
This free z score calculator helps you get accurate results instantly without needing to work through the math manually. Whether you need a quick estimate or a precise figure, having a reliable tool on hand saves time and reduces errors compared to manual calculation.
How to Use This Calculator
- Enter your values in the input fields above. Each field is labeled to guide you.
- Double-check your inputs — results are only as accurate as the numbers you enter.
- Click the Calculate button to see your result instantly.
- Use the result for your planning, budgeting, or decision-making.
Why Accurate Calculations Matter
Small errors in math calculations can compound into significant problems. A 1% miscalculation in a budget or measurement can translate to hundreds or thousands of dollars in wasted resources, or result in having to redo work entirely. This calculator uses the standard formulas and methods to give you reliable results you can trust.
Tips for Getting the Best Results
- Use consistent units throughout (all in feet, all in dollars, etc.)
- For estimates, add a 10% buffer to account for real-world variables
- Save your result by taking a screenshot or writing it down before closing the page
- For decisions involving significant money or safety, verify results with a qualified professional
Frequently Asked Questions
Is this calculator free? Yes — completely free with no account, login, or payment required. Use it as many times as you need.
How accurate are the results? This calculator uses the standard formulas for z score calculations. Results are accurate for typical use cases. For specialized or high-stakes applications, consult a professional.
Does it work on mobile? Yes. This calculator is fully responsive and works on smartphones, tablets, and desktops.