Percentage Difference and Percent Error Calculator
Choose percentage difference for two values with no starting point, or percent error to compare a measurement with an accepted value. The change from one value to the other is shown for comparison.
Percentage difference divides by the average of the two values. Percent error divides by the accepted value.
Worked examples
Percentage difference
50 and 70
33.33%
The gap of 20 divided by the average of 60.
Percent error
Measured 9.5, accepted 9.81
3.16% (signed -3.16%)
0.31 ÷ 9.81 × 100.
About Percentage Difference and Percent Error Calculator
Two different questions are often called a percentage difference. The first compares two values when neither is the original or the right answer, for example the prices of two similar products. It is the gap between the values divided by their average, times 100, so it does not matter which you list first. The second is percent error, which compares a measurement with a value known to be correct, and divides by that accepted value instead.
Choose the option that matches your problem. For two values such as 50 and 70, the percentage difference is 33.3%, because the gap of 20 is divided by the average of 60. The percentage change from 50 to 70 is 40%, because you divide by the starting value, and the page shows both so that you can see the distinction. For a measurement of 9.5 against an accepted 9.81, the percent error is 3.16% in size, and negative when signed, because the measurement was low.
How to use Percentage Difference and Percent Error Calculator
- Choose percentage difference or percent error.
- Enter the first value, or your measured value.
- Enter the second value, or the accepted value.
- Read the percentage and follow the working beneath it.
Common uses
- Comparing two prices or two measurements fairly
- Reporting percent error in a science practical
- Checking the accuracy of an instrument
- Comparing results from two surveys or two years
Frequently asked questions
What is the formula for percentage difference?
It is the size of the difference between the two values divided by their average, times 100. For 50 and 70 that is 20 divided by 60, times 100, which is 33.3%.
What is the formula for percent error?
It is the measured value minus the accepted value, divided by the accepted value, times 100. Most teachers want the size without the sign, which is the absolute percent error.
How is percentage difference different from percentage change?
Percentage change treats one value as the starting point and divides by it. Percentage difference treats both values equally and divides by their average, so it gives the same answer in either order.
Can percent error be negative?
Yes. The signed value is negative when you measured less than the accepted value. The absolute value, which ignores the sign, is the figure usually reported.
What happens if the accepted value is zero?
Percent error cannot be worked out, because it would mean dividing by zero. The page asks you to check the value.