How to Calculate Stdev in Excel

by

Excel Standard Deviation Calculator

Sample (STDEV.S) – Part of a group Population (STDEV.P) – Entire group

Calculation Results

Count (n):

Mean (Average):

Variance:

Standard Deviation:

function calculateSD() { var rawData = document.getElementById('dataset').value; var type = document.getElementById('calcType').value; var errorDiv = document.getElementById('error-msg'); var resultsDiv = document.getElementById('results-box'); errorDiv.style.display = 'none'; resultsDiv.style.display = 'none'; // Clean data var numbers = rawData.split(/[\s,]+/).filter(function(x) { return x.length > 0 && !isNaN(parseFloat(x)); }).map(Number); if (numbers.length < 2) { errorDiv.innerHTML = "Please enter at least two numeric values to calculate standard deviation."; errorDiv.style.display = 'block'; return; } // Calculation Logic var n = numbers.length; var sum = 0; for (var i = 0; i < n; i++) { sum += numbers[i]; } var mean = sum / n; var squareDiffSum = 0; for (var j = 0; j < n; j++) { squareDiffSum += Math.pow(numbers[j] – mean, 2); } var variance; if (type === 'sample') { variance = squareDiffSum / (n – 1); } else { variance = squareDiffSum / n; } var stdev = Math.sqrt(variance); // Display document.getElementById('res-count').innerText = n; document.getElementById('res-mean').innerText = mean.toFixed(4); document.getElementById('res-variance').innerText = variance.toFixed(4); document.getElementById('res-stdev').innerText = stdev.toFixed(4); resultsDiv.style.display = 'block'; }

How to Calculate Standard Deviation in Excel

Standard deviation is a critical statistical measure that quantifies the amount of variation or dispersion in a set of values. In Microsoft Excel, calculating this value is automated via specific functions, but understanding which formula to use is essential for data accuracy.

The Two Main Excel Formulas

Depending on your data source, Excel provides two primary functions:

  • STDEV.S: This function calculates the standard deviation based on a sample. Use this when your data represents only a portion of the entire group (e.g., surveying 100 customers out of 10,000).
  • STDEV.P: This function calculates the standard deviation for the entire population. Use this when you have every single data point for the group you are analyzing (e.g., the test scores of every student in a specific classroom).

Step-by-Step Instructions

  1. Prepare your data: List your numbers in a single column or row (e.g., cells A1 through A10).
  2. Select the output cell: Click on the empty cell where you want the result to appear.
  3. Type the formula: Enter =STDEV.S(A1:A10) for a sample or =STDEV.P(A1:A10) for a population.
  4. Press Enter: Excel will immediately calculate the result.

Real-World Example

Imagine you are tracking the daily sales of a small boutique over 5 days: 120, 150, 110, 190, and 130. To find out how much these sales vary from the average:

  • Mean (Average): 140
  • Sample Standard Deviation (STDEV.S): 31.62

A high standard deviation indicates that the data points are spread far from the mean, while a low standard deviation indicates that they are clustered closely around the average.

Why Does n-1 Matter?

When using the sample formula (STDEV.S), Excel uses "Bessel's Correction" (dividing by n-1 instead of n). This corrects the bias in the estimation of the population variance, providing a more accurate reflection of the total group's variability when only a small portion is known.

Leave a Comment