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Average Percentage Calculator – Simple & Weighted Averages

The Average Percentage Calculator solves one of the most common statistical errors: averaging percentages with unequal sample sizes. When data groups have different totals (e.g. 90% out of 100 students vs 50% out of 10 students), calculating a simple average yields mathematically false conclusions (Simpson’s Paradox). This tool allows you to add multiple percentage rows, assign weights or group sizes, and compute both simple and weighted averages instantly.

Average Percentage Calculator

Compute simple and weighted averages of percentages with unequal sample sizes or weights

Percentage Data Rows (3)
%
Weight:
%
Weight:
%
Weight:
Weighted Average3 Data Points
82.70%

High precision: 82.7000%

Weighted Average:82.70%
Simple Unweighted Average:83.67%
Total Weights Sum:100
Mathematical Note: The Average of Percentages Rule

You can only compute a simple average of percentages if all groups have the exact same sample size or weight. When groups differ in size (e.g. 90% of 1,000 students vs 50% of 10 students), taking a simple average yields mathematically false conclusions (Simpson’s Paradox). Always use the Weighted Average method for real-world datasets.

Weighted Average of Percentages Formula

How this mathematical and clinical model is calculated

Weighted Average = (Sum of (Percentage_i * Weight_i)) / (Sum of Weights)

Multiplies each percentage by its sample size or weight, sums the products, and divides by the total weight.

Step-by-Step Calculation Process:

1

Add percentage items and their respective weights or sample sizes.

2

Choose Weighted Average or Simple Unweighted Average mode.

3

Review exact percentage result and total weights summary.

Key Capabilities & Features

Dynamically add, edit, or remove unlimited data rows
Supports both simple unweighted and sample-size weighted calculations
Protects against Simpson’s Paradox statistical distortions
One-click summary copy to clipboard

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Help & FAQ

Frequently Asked Questions: Average Percentage Calculator – Simple & Weighted Averages

Everything you need to know about tools in this section.

Only if all percentages represent identical sample sizes. If Group A has 90% (out of 1,000 people) and Group B has 10% (out of 10 people), the simple average (90 + 10)/2 = 50% is mathematically incorrect. The true weighted average is (900 + 1) / 1,010 = 89.2%.