Probability Calculator — Compute the Chance of an Event
Calculate event probability: classical, complement, two independent and “at least one”. Free chance calculator in percent and as a decimal fraction.
Statistics Calculators
Analyse data statistically: mean, median, mode, standard deviation, variance and Pearson correlation.
Mean, Median and Mode Calculator
Calculate the mean, median, mode, range, sum and count for any set of numbers. Enter values separated by commas or spaces. Free, instant, no signup required.
Standard Deviation Calculator
Calculate standard deviation and variance for a sample or population. Enter numbers separated by commas — instant result, no signup needed.
Variance and Standard Deviation Calculator
Calculate variance and standard deviation for a sample or population. Free statistics calculator with formula explanation and worked examples.
Percentile and quartile calculator
Calculate any percentile, quartiles Q1 Q2 Q3 and interquartile range IQR for your own dataset. Uses PERCENTILE.INC linear interpolation method — fast and free.
Z-Score Calculator
Calculate the z-score (standardized value) and its corresponding percentile in the normal distribution. Enter the value, mean and standard deviation — instant result.
Pearson Correlation Calculator
Calculate the Pearson correlation coefficient (r) and coefficient of determination (r2) for two data series. Enter values separated by commas — instant result with interpretation, no signup needed.
Sample Size Calculator
Calculate the minimum sample size for surveys and research. Choose confidence level, margin of error and expected proportion — instant result, no sign-up required.
Confidence Interval Calculator
Calculate the confidence interval for a mean or proportion. Choose 90%, 95% or 99% confidence level, enter sample mean, standard deviation and sample size — instant result.
Chi-Square Test Calculator (χ²)
Calculate the χ² statistic, degrees of freedom and p-value for a chi-square goodness-of-fit test. Enter observed and expected frequencies — instant result.
Linear Regression Calculator
Free online linear regression calculator. Compute slope a, intercept b, R² coefficient, and predict Y for any X value. Fast and accurate.
One-Sample T-Test Calculator
Calculate the t-statistic and check statistical significance of the difference between a sample mean and an expected value. Free online one-sample t-test calculator.
Standard Error Calculator
Calculate the standard error of the mean (SEM) and the 95% confidence interval. Enter the mean, standard deviation and sample size — instant result.
Descriptive statistics — online calculators
Statistics is the language that turns data into knowledge. The statistics calculators on Liczbnik.pl bring together the most important descriptive measures and tests in one place — no R installation or Excel pivot tables required. The arithmetic mean (x̄) is the sum of values divided by their count. For skewed data, the median is a better measure of central tendency because it is resistant to outliers: sort the dataset and pick the middle value (or average the two middle values for an even count). The mode — the most frequently occurring value — is useful for categorical data analysis. Standard deviation (σ or s) quantifies how much values spread around the mean. Low standard deviation signals a tight, consistent dataset; high standard deviation means high variability. Key distinction: population variance divides by N; sample variance divides by N−1 (Bessel's correction), producing an unbiased estimator when working with sampled data. Pearson correlation (r) measures the strength and direction of the linear relationship between two quantitative variables. Values from +0.7 to +1.0 indicate a strong positive correlation; −0.7 to −1.0 a strong negative one; near 0 means no linear association. Remember: correlation does not imply causation. A p-value below 0.05 is the conventional threshold for statistical significance (α = 5%) — it means there is less than a 5% probability that the result occurred by chance. The 95% confidence interval is the range within which the true population parameter lies with 95% certainty: x̄ ± 1.96 × (s/√n) for large samples. For basic analysis these calculators are sufficient; for advanced work use R, Python (pandas/scipy) or SPSS.
Frequently asked questions about statistics
How to calculate the arithmetic mean?
Mean = sum of all values / number of values. E.g. (2+4+6) / 3 = 4.
What is the median?
The median is the middle value of a sorted dataset. For an even count, it is the average of the two middle values.
What is the mode?
The mode is the most frequently occurring value in a dataset.
How to calculate standard deviation?
Standard deviation = square root of variance = square root of the mean of squared deviations from the mean.
What is Pearson correlation?
Pearson correlation (r) measures the strength of a linear relationship between two variables: from −1 to +1.
What is the difference between population and sample variance?
Population variance divides by N; sample variance divides by N−1 (Bessel's correction for unbiasedness).
How to interpret a p-value?
A p-value < 0.05 means the result is statistically significant at the α = 5% significance level.
What is a percentile?
Percentile X is the value below which X% of observations fall. E.g. the 90th percentile is the threshold below which 90% of data lies.
How to calculate a confidence interval?
95% confidence interval = mean ± 1.96 × (std. dev. / √n) for large samples.
Does the statistics calculator replace software?
For basic calculations — yes. For advanced analysis, use R, Python (pandas) or SPSS.