Confidence Interval Calculator
Calculate a z-based confidence interval for a mean using sample mean, sample standard deviation, sample size, and confidence level.
Formula:
CI = mean ± z* · (sd / √n)
| Metric | Value |
|---|
Privacy: calculations run locally in your browser. No inputs are stored or transmitted.
How it works
This tool uses common z critical values: 1.645 for 90%, 1.96 for 95%, 2.576 for 99%.
Examples
- mean = 70, sd = 12, n = 100, 95%
- Standard error = sd / √n
- Margin of error = z* × standard error
When to use this tool
This tool is designed for quick, practical tasks such as everyday calculations, data formatting, or simple conversions. It is best used when you need fast results without installing software or using complex tools.
When to use
- Quick checks or one-time calculations
- Validating or converting data before using it elsewhere
- Simple tasks that do not require advanced software
When not to use
- Critical financial, legal, or medical decisions
- Large-scale or automated processing
- Situations requiring guaranteed precision beyond basic validation
Always review results before using them in important contexts.
About this tool
This tool helps you perform quick utility operations directly in your browser. It runs entirely in your browser without sending data to a server.
You can use this tool when handling simple tasks without installing additional software. The results should be interpreted as a processed output based on your input data.
FAQ
- What does this confidence interval calculator compute?
It computes a z-based confidence interval for a mean using sample mean, sample standard deviation, sample size, and selected confidence level.
- What confidence levels are supported?
This page supports common z-based levels such as 90%, 95%, and 99%.
- Why must sample size be greater than 0?
Because the standard error uses the square root of sample size in the denominator.
- Are calculations stored?
No. Everything runs locally in your browser.