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Percent Difference Calculator

Percent difference is used when comparing two experimental or observed numbers of equal standing where neither value is considered the "original" or "

Mathematics
Formula & Methodology
Percent Difference = (|V₁ - V₂| ÷ ((V₁ + V₂) ÷ 2)) × 100% Average = (V₁ + V₂) ÷ 2 Absolute Difference = |V₁ - V₂|

To compute percent difference between two numbers V₁ and V₂: 1. Subtract the two numbers and take the absolute value |V₁ - V₂| to get the positive distance between them. 2. Find the average of the two numbers by adding them together and dividing by 2. 3. Divide the absolute difference by the average, then multiply by 100%. Because the average serves as the denominator, the order in which you enter V₁ and V₂ produces the exact same percent difference.

Percent Difference

18.18%

Overview

Percent difference is used when comparing two experimental or observed numbers of equal standing where neither value is considered the "original" or "true" baseline. This free Percent Difference Calculator compares two values by dividing their absolute difference by their arithmetic average.

Unlike percentage change or percentage error (which require an established reference or starting point), percent difference treats both values symmetrically. It is standard in physics laboratories, chemistry experiments, manufacturing tolerances, and data auditing.

Worked Examples

Example 1: Comparing Experimental Measurements (25 vs 30)

Inputs: V₁ = 25, V₂ = 30

  1. Absolute difference: |25 - 30| = 5.
  2. Average: (25 + 30) ÷ 2 = 27.5.
  3. Divide difference by average: 5 ÷ 27.5 = 0.181818.
  4. Multiply by 100: 18.18%.
Final Answer: 18.18%

Example 2: Lab Density Measurements (1.24 vs 1.28 g/cm³)

Inputs: V₁ = 1.24, V₂ = 1.28

  1. Absolute difference: |1.24 - 1.28| = 0.04.
  2. Average: (1.24 + 1.28) ÷ 2 = 1.26.
  3. Divide: 0.04 ÷ 1.26 = 0.03175.
  4. Multiply: 3.17%.
Final Answer: 3.17%

Example 3: Factory Part Dimensions (10.2 mm vs 9.8 mm)

Inputs: V₁ = 10.2, V₂ = 9.8

  1. Difference: |10.2 - 9.8| = 0.4.
  2. Average: (10.2 + 9.8) ÷ 2 = 10.0.
  3. Percentage: (0.4 ÷ 10.0) × 100 = 4.0%.
Final Answer: 4.00%

How to Use This Calculator

  1. Enter the first measured quantity in the V₁ field.
  2. Enter the second measured quantity in the V₂ field.
  3. Click "Calculate" to evaluate the percent difference.
  4. Review the absolute difference and midpoint average below.
  5. Click "Reset" to compare two new numbers.

Reference Table

Value 1Value 2Absolute DifferencePercent Difference
1012218.18%
2530518.18%
50601018.18%
100110109.52%
1001202018.18%
500550509.52%

Frequently Asked Questions

How does percent difference differ from percent change?
Percent change is directional and uses the initial value as the denominator: (New - Old) ÷ Old. Percent difference has no direction and divides by the average of both numbers.
Does the order of the numbers matter?
No. Because the formula uses absolute difference and the symmetric average of the two numbers, swapping V₁ and V₂ produces identical results.
What is the maximum possible percent difference?
For two positive numbers where one is near zero and the other is positive, the maximum theoretical percent difference approaches 200%.
What is percent error?
Percent error compares an experimental measurement against an accepted theoretical standard: |Experimental - Theoretical| ÷ |Theoretical| × 100%.
Can negative values be used in percent difference?
The formula mathematically permits negative values as long as their sum (V₁ + V₂) does not equal zero. However, percent difference is most intuitively applied to positive physical quantities.

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Reviewed & Authored by: Dr. Elizabeth Vance, PhD Applied Mathematics · Last Updated: 2026-10-06
Computed via symmetric midpoint normalisation per NIST experimental physics protocols.