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CONFIDENCE.NORM Function
Summary
The CONFIDENCE.NORM function calculates the confidence interval margin for a population mean using the normal distribution assumption. It helps determine a range around your sample mean where the true population mean is likely to fall with a specified confidence level.
Syntax
CONFIDENCE.NORM(alpha, standard_dev, size)Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
| alpha | Number |
Yes | Significance level used to compute confidence. Confidence level = 100*(1-alpha)% |
| standard_dev | Number |
Yes | Population standard deviation (assumed known, must be positive) |
| size | Number |
Yes | Sample size (integer ≥ 1) |
Using the CONFIDENCE.NORM Function
Use CONFIDENCE.NORM when you know the population standard deviation and want to construct confidence intervals around your sample mean. Add and subtract the result from your sample mean to get the full confidence interval range. Ideal for quality control, survey analysis, and scientific research.
Common CONFIDENCE.NORM Examples
Basic Confidence Interval
=CONFIDENCE.NORM(0.05, 2.5, 50)Returns 0.692952, meaning the true population mean is within ±0.69 of the sample mean with 95% confidence (assuming sample mean of 30 minutes)
Survey Analysis
=CONFIDENCE.NORM(0.01, 15, 200)Calculates 99% confidence interval margin for a survey of 200 people with population std dev of 15
Quality Control
=CONFIDENCE.NORM(0.05, 0.8, 100)95% confidence margin for production measurements (sample of 100, pop std dev 0.8)
Frequently Asked Questions
Common Errors and Solutions
#VALUE!
Cause: Any argument is non-numeric
Solution: Ensure all inputs are valid numbers
#NUM!
Cause: alpha ≤ 0 or ≥ 1
Solution: Use alpha between 0 and 1 (e.g., 0.05 for 95% confidence)
#NUM!
Cause: standard_dev ≤ 0
Solution: Population standard deviation must be positive
#NUM!
Cause: size < 1
Solution: Sample size must be at least 1
Notes
- If size is not integer, Excel truncates it downward
- Assumes normal distribution of population
- Population standard deviation must be known in advance
- Result is half-width of confidence interval (add/subtract from sample mean)
- Perfect for large samples where normal approximation is valid
Compatibility
Available in: Excel 2010, Excel 2013, Excel 2016, Excel 2019, Excel 2021, Microsoft 365
Not available in: Excel 2007, Excel 2003, Earlier versions
Content last reviewed: December 9, 2025
Update frequency: As needed
Excel versions tested: Excel 2010+