Confidence Interval Calculator vs Sample Size Calculator
Two calculators for the same neighbourhood of questions. Here is what each measures, what you feed in, and where you'd reach for one over the other.
Confidence Interval Calculator
Compute the lower and upper bounds of a confidence interval for a population mean using a sample mean, the standard error of that mean, and a critical z-value (1.645 / 1.96 / 2.576 for 90% / 95% / 99% confidence). This is the standard way to report uncertainty around survey results, lab measurements, or any sample-based estimate.
- Answers
- Lower Bound
- Inputs
- Sample Mean, Standard Error, Z-Value
Sample Size Calculator
Calculate the minimum number of respondents needed to estimate a population proportion within a given margin of error at a chosen confidence level — the standard formula behind almost every survey, poll, and quality audit. Includes the finite-population correction so you can plan surveys of small populations without over-sampling.
- Answers
- Required Sample Size
- Inputs
- Population Size, Confidence Level, Margin of Error
At a glance
| Confidence Interval Calculator | Sample Size Calculator | |
|---|---|---|
| Category | Statistics | Statistics |
| Answers | Lower Bound | Required Sample Size |
| Inputs | 3 | 3 |
| Result unit | — | — |
When to use each
Compute the lower and upper bounds of a confidence interval for a population mean using a sample mean, the standard error of that mean, and a critical z-value (1.645 / 1.96 / 2.576 for 90% / 95% / 99% confidence). This is the standard way to report uncertainty around survey results, lab measurements, or any sample-based estimate.
Calculate the minimum number of respondents needed to estimate a population proportion within a given margin of error at a chosen confidence level — the standard formula behind almost every survey, poll, and quality audit. Includes the finite-population correction so you can plan surveys of small populations without over-sampling.