How to use this calculator
- Enter your own values in the labeled fields. Check the units and assumptions before comparing results. Only the fields needed for your selected calculation mode are shown.
- Your answer updates automatically. Review the calculation steps to see exactly how it was calculated.
- Copy, share, save, or download your result. Saved inputs stay on this device.
How the calculation works
Use t when the population standard deviation is estimated from the sample; select z only when population sigma is known. Proportion mode uses observed successes and sample size, producing a Wilson interval bounded by 0 and 1. Inference depends on the sampling assumptions. Review the units, period and assumptions before comparing scenarios. Displayed values are rounded, while the underlying calculation retains its available precision.
A worked example
For mean=100, sample SD=15 and n=25, a 95% t interval is approximately 93.8083 to 106.1917.
Reading your result
Use the main result together with its units and supporting figures. Display values are rounded; calculations keep their underlying precision. A change in inputs or assumptions can change the answer. Compare the step-by-step working with your intended use before relying on an estimate.
Frequently asked questions
What assumptions does this calculation use?
Use t when the population standard deviation is estimated from the sample; select z only when population sigma is known. Proportion mode uses observed successes and sample size, producing a Wilson interval bounded by 0 and 1. Inference depends on the sampling assumptions.
Can I save or check a scenario?
The result includes the working and supporting values. Save and Restore keep inputs on this device; Copy, Download and Print export the result. Sharing a scenario explicitly includes the inputs in its link.
Sources & methodology
NIST: statistical confidence intervals ↗
Formula review: October 24, 2026. Read our methodology.