Determine the confidence level
Find the critical value for that confidence level
Identify the standard deviation or sample proportion
Identify the sample size
Calculate the standard error
Multiply the critical value by the standard error
Use the formula: Margin of Error = Critical Value × Standard Error
For a mean: Margin of Error = z or t × (standard deviation ÷ square root of sample size)
For a proportion: Margin of Error = z × square root of [p(1 – p) ÷ sample size]