Confidence Interval Calculator
Enter your sample mean, standard deviation and sample size, pick 90, 95 or 99 percent confidence, and get the margin of error plus both interval limits — a standard Z-interval tool for research and statistics coursework.
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How to use
- Enter the sample mean, standard deviation and sample size.
- Select a confidence level — 95% is the most common in research.
- The margin of error and both interval limits are shown below.
Note: This is a Z interval — when the population standard deviation is known, or the sample is large (n >= 30), this is the standard method. For small samples (n < 30) with unknown sigma, use the t interval, whose critical values come from the t table.
Tips
- 95% is the standard choice in most research; use 99% when you need extra caution.
- Larger samples shrink the margin of error — that is why big surveys are trusted.
- This is a Z interval: use a t-interval for small samples with unknown standard deviation.
- The interval estimates the population mean, not the range of individual values.