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Confidence Interval for Mean
Calculate the confidence interval for a population mean based on sample data.
Sample Size Calculator
Calculate how many samples you need for a desired margin of error.
Confidence Interval for Proportion
Calculate the confidence interval for a population proportion (e.g., survey results, success rates).
Confidence Interval Calculator
Calculate statistical confidence intervals for your data
What is Confidence Interval Calculator?
Confidence Interval Calculator helps you understand how reliable your sample data is. It tells you the range where the true average of a whole population likely falls, based on a smaller sample you measured.
Why Would You Need Confidence Intervals?
Whenever you can't measure everyone or everything, confidence intervals help you draw conclusions:
- Survey research: Poll 1,000 people to estimate what millions think
- Quality testing: Test 100 products to judge the quality of 10,000
- Medical studies: Study a group of patients to understand treatment effects
- Market research: Sample customers to understand buying behavior
- Academic research: Make statistical claims in papers and theses
How to Calculate Confidence Intervals - Step by Step
- Choose calculation type: Pick "Mean CI" for averages or "Proportion CI" for percentages
- Enter your data: Input sample size, mean (or proportion), and standard deviation
- Select confidence level: Choose from 70% to 99.9% (95% is most common)
- Read your results: See the lower and upper bounds plus margin of error
Key Features
- Multiple confidence levels: Choose from 70%, 80%, 90%, 95%, 99%, or 99.9%
- Sample size calculator: Find out how many responses you need for your survey
- Proportion CI: Calculate intervals for yes/no survey questions
- Real-time calculation: Results update as you type - no submit button needed
- Margin of error: See exactly how precise your estimate is
Tips for Best Results
- Use 95% confidence level for most purposes - it's the standard in research
- Larger samples give narrower (more precise) intervals
- Use the sample size calculator before collecting data to plan your study
Frequently Asked Questions
What does 95% confidence mean?
It means if you repeated your study 100 times with new samples, about 95 of those intervals would contain the true population value.
How big should my sample be?
Use our Sample Size Calculator tab! Generally, 30+ is minimum, but hundreds are better for narrow intervals.
When should I use Proportion CI vs Mean CI?
Use Proportion CI for yes/no questions (like "Did you vote?"). Use Mean CI for measurements (like average height or income).