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Confidence Interval Calculator
Quickly calculate your confidence intervals with our easy-to-use tool.
About This Tool
So, you’ve got some data, you ran an experiment, or maybe you’re just curious about how sure you can be about a sample mean. That’s where a confidence interval comes in. This calculator helps you figure out a range—not just a single number—that likely contains the true population mean, based on your sample. It’s not magic, but it’s pretty close. I built this because I got tired of digging through stats textbooks every time I needed to check a margin of error. Whether you’re analyzing survey results, test scores, or customer feedback, this tool gives you a quick, no-nonsense way to estimate how much you can trust your sample. It uses the standard formula for confidence intervals, assuming a normal distribution (or large enough sample size for the Central Limit Theorem to kick in). You plug in your sample mean, standard deviation, sample size, and confidence level—say, 95%—and it spits out the interval. Simple.Key Features
- Calculates confidence intervals for population means using sample data
- Supports common confidence levels: 90%, 95%, and 99%
- Handles both known and unknown population standard deviations (z and t-distribution)
- Clear, step-by-step breakdown so you know exactly how the result was calculated
- Works with raw data or summary statistics—your choice
- No sign-up, no ads, no nonsense. Just input, click, and go
- Mobile-friendly, so you can use it on your phone during fieldwork or meetings
FAQ
Wait, what’s the difference between a 95% and 99% confidence level?
Great question. A 95% confidence interval means that if you took 100 different samples and built an interval each time, about 95 of them would contain the true population mean. The 99% interval is wider—it’s more confident, but less precise. So you trade off certainty for range. Most people use 95% because it’s a solid middle ground.
Can I use this if my sample size is small?
Yes, but with a caveat. If your sample is under 30 and the population standard deviation isn’t known, the calculator automatically switches to the t-distribution, which accounts for extra uncertainty. That’s more accurate for small samples. Just don’t expect miracles if you only have 5 data points—garbage in, garbage out, as they say.