This confidence interval reference table shows the margin of error for a range of sample mean values, assuming a standard deviation of 15, a sample size of 30 and a confidence level of 95% (z = 1.96). Every figure is computed with the same engine that powers our Confidence Interval Calculator, so the numbers are exact.
| Sample mean | Margin of error | Lower bound | Upper bound |
|---|---|---|---|
| 25 | 5.368 | 19.632 | 30.368 |
| 50 | 5.368 | 44.632 | 55.368 |
| 75 | 5.368 | 69.632 | 80.368 |
| 100 | 5.368 | 94.632 | 105.368 |
| 150 | 5.368 | 144.632 | 155.368 |
| 200 | 5.368 | 194.632 | 205.368 |
| 300 | 5.368 | 294.632 | 305.368 |
| 500 | 5.368 | 494.632 | 505.368 |
| 700 | 5.368 | 694.632 | 705.368 |
| 1,000 | 5.368 | 994.632 | 1,005.368 |
How to use this table
Find the row closest to your sample mean and read across to the margin of error. For a value between two rows, the real figure sits between them — or enter your exact numbers in the Confidence Interval Calculator for a precise answer.
Need a value that is not in the table? — the Confidence Interval Calculator does it instantly, for free, with the formula and a worked example built in.
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