Enter your sample mean, standard deviation and sample size to calculate the margin of error and confidence interval at your chosen confidence level.
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The margin of error is calculated as the z-score for your chosen confidence level multiplied by the standard error (standard deviation ÷ square root of sample size). The confidence interval is then the sample mean plus and minus that margin of error, giving a range you can be reasonably confident contains the true population mean.
It means that if you repeated your sampling process many times, about 95% of the resulting intervals would contain the true population mean. It doesn't mean there's a 95% chance the true mean falls in this specific interval.
The margin of error divides by the square root of sample size, so larger samples produce smaller standard errors and, therefore, narrower, more precise confidence intervals.
Z-Score Calculator
Calculate a z-score and percentile from a value, mean and standard deviation.
Sample Size Calculator
Calculate the survey sample size needed for a target confidence level and margin of error.
Standard Deviation Calculator
Calculate mean, variance and standard deviation from a data set.
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