Basic Statistics
Z-Score Calculator
Upload a CSV file or enter values to calculate z-scores and approximate normal probabilities.
← Back to Tools
Upload CSV, Use Example Data, or Enter Values
Choose the calculation that matches your question. An individual z-score uses one observation. A sample mean z-score uses the sample mean and standard error. Standardize column calculates a z-score for every uploaded value.
Interpretation
A z-score measures distance in standard deviation units, but the correct formula depends on what is being standardized.
Individual observation: z = (x - μ) / σ
Sample mean / one-sample z: z = (x̄ - μ) / (σ / √n)
If you compare this page with another calculator, confirm whether that calculator is using one observation, a sample mean, or a standardized column. Those produce different but valid results.