Math
How to Calculate Percent Error: A Quick Tutorial for Students With Real Examples
Author:
Nicole Hardy
Apr 10, 2025
10 min
Table of contents
- What Is Percent Error?
- The Formula: How to Calculate Percent Error
- How to Calculate Percent Error in Chemistry
- How to Calculate Percent Error in Physics
- How to Calculate Percent Error in Excel
- Using Tools: From Basic Calculator to Online Help
- Common Mistakes to Avoid
- Bonus: Relative Error vs. Percent Error
- Before You Go
If you’re a student working on lab reports or math problems, you’ve probably come across the term percent error. It’s one of those concepts that pops up in chemistry, physics, and even statistics—but many students still get stuck trying to remember the formula or how to apply it correctly.
No worries! This guide breaks it down into simple steps and offers real examples you can use as a reference. Whether you need to know how to calculate percent error in chemistry, physics, or even in a spreadsheet, this tutorial has you covered. And yes, you can do it all with just a basic calculator—no fancy tools required.
What Is Percent Error?
Percent error is a way to measure how close your measured or experimental value is to the actual or accepted value. It’s used to show accuracy—how far off you are from the “true” result. The smaller the percent error, the more accurate your measurement.
This is especially useful when you’re comparing lab data to theoretical results, like in science experiments or math calculations.
The Formula: How to Calculate Percent Error
Let’s get to the core of it: how to calculate percent error. Here’s the standard formula you’ll use in almost every subject:
You subtract the actual (or accepted) value from the measured (or experimental) value, take the absolute value of the difference (so the result is always positive), divide by the actual value, and then multiply by 100 to turn it into a percentage.
This works across the board—whether you’re figuring out how to calculate percent error in chemistry, physics, or general science.
How to Calculate Percent Error in Chemistry
In chemistry labs, accuracy is key. Whether you’re titrating a solution or measuring molar mass, knowing how to calculate the percent error in chemistry helps determine whether your results are reliable.
Example:
- Actual value (accepted mass): 18.02 g/mol
- Measured value (your result): 17.75 g/mol
Understanding how to calculate percent error chemistry helps when you’re writing lab reports or interpreting experimental data. It’s also great for identifying whether human error or equipment might have caused the discrepancy.
How to Calculate Percent Error in Physics
In physics, precision is everything. Whether you’re calculating acceleration, force, or speed, knowing how to calculate percent error in physics shows how accurate your calculations are compared to theoretical values.
Example:
- Actual value: 9.81 m/s² (acceleration due to gravity)
- Measured value: 9.65 m/s²
So, if you’re wondering how to calculate percent error physics-style, it’s the same process—just applied to physical quantities like mass, velocity, or energy.
How to Calculate Percent Error in Excel
If you’re working with large datasets or doing multiple trials, it’s helpful to know how to calculate for percent error in Excel.
Here’s how to set up a basic formula:
- In column A, list the actual values.
- In column B, list the measured values.
- In column C, use this formula:
That will give you the percent error in column C. This is especially helpful for repeated trials in labs or math exercises.
Using Tools: From Basic Calculator to Online Help
If you’re not a fan of manual calculations, you can also use a basic calculator to punch in the numbers step by step. Just remember to use absolute value and convert your final number into a percentage.
There are also online tools like a percent error calculator, which do the math for you. All you need to do is enter the actual and measured values, and it instantly gives you the answer—super useful during homework crunch time or lab write-ups.
Common Mistakes to Avoid
While learning how to calculate percent of error might seem straightforward, here are a few pitfalls to watch out for:
- Using the wrong values: Always subtract the measured value from the actual one.
- Forgetting absolute value: Percent error should always be positive.
- Dividing by the wrong number: You must divide by the actual value, not the measured one.
- Forgetting to multiply by 100: This turns your decimal into a percentage.
Mastering how to calculate a percent error is as much about avoiding small errors as it is about understanding the concept.
Bonus: Relative Error vs. Percent Error
Ever been asked how to calculate percent relative error? It’s similar to percent error but is usually used when there’s no known or actual value. Instead, it compares errors relative to the measured value or average.
For now, stick with percent error unless your instructor asks otherwise.
Before You Go
Learning how to calculate the percent error isn’t just about getting the right answer—it’s about understanding how reliable your data really is. Whether you’re in the lab, classroom, or studying from home, this simple skill can help you impress your teachers, sharpen your analysis, and ace those reports.