How To Calculate Uncertainty In Physics?

By A2Z Calculators | Last update: 26 December 2023

In the realm of physics, precision is paramount. Every measurement comes with a level of uncertainty, a margin of potential error that needs to be carefully considered.

In this guide, we will explore the fundamentals of how to calculate uncertainty in physics, providing you with a clear understanding of the process and the tools involved.

Why Calculate Uncertainty?

Knowing the uncertainty associated with a measurement is crucial for two main reasons:

Precision Assessment: Understanding the range within which a measurement is likely to fall helps in assessing the precision of experimental results.

Comparison and Communication: When sharing scientific findings, expressing uncertainty ensures that others can evaluate the reliability of the data and make informed comparisons.

How to Calculate Uncertainty in Physics

1. Standard Deviation: The Foundation of Uncertainty

The standard deviation is a fundamental tool for calculating uncertainty. It measures the spread of a set of measurements around their mean (average). The formula is relatively simple:

$$ \sigma = \sqrt{\frac{\sum{(x_i – \bar{x})^2}}{N-1}} $$


  • σ is the standard deviation,
  • xi represents each individual measurement,
  • x¯ is the mean,
  • N is the number of measurements.

2. Percentage Uncertainty: Putting It Into Perspective

Expressing uncertainty as a percentage is a practical way to communicate its significance. The formula is straightforward:

$$ \% \text{ Uncertainty} = \left( \frac{\text{Uncertainty}}{\text{Measured Value}} \right) \times 100 $$

This gives a clear representation of the relative magnitude of uncertainty in relation to the measured value.

3. Propagation of Uncertainty: Dealing with Derived Quantities

When dealing with calculations involving multiple measured quantities, the propagation of uncertainty comes into play. The general formula is:

$$ \delta Q = \sqrt{\left(\frac{\partial Q}{\partial x_1} \delta x_1\right)^2 + \left(\frac{\partial Q}{\partial x_2} \delta x_2\right)^2 + \ldots} $$

Here, Q is the derived quantity, x1,x2,… are the measured quantities, and δx1, δx2,… are their respective uncertainties.

4. Maximum Error: Understanding Equipment Limitations

In some cases, the maximum error of measurement is provided by the manufacturer or determined through calibration. This value represents the largest possible error due to limitations in the measurement apparatus or method.

Solving Uncertainty: A Step-by-Step Guide

Gather Your Data: Take multiple measurements of the quantity you are interested in.

Calculate the Mean: Find the average of your measurements.

Compute the Standard Deviation: Use the standard deviation formula to quantify the spread of measurements.

Express as Percentage Uncertainty: Convert the standard deviation to a percentage to understand the relative uncertainty.

Propagate Uncertainty (if needed): For derived quantities, apply the propagation of uncertainty formula.

Consider Maximum Error: Take into account the maximum error associated with your measurement equipment.

Common Pitfalls and Tips

Pitfalls to Avoid

Ignoring Systematic Errors: Systematic errors, consistent inaccuracies in measurements, should not be overlooked.

Misinterpreting Precision for Accuracy: A precise measurement does not guarantee accuracy. Be cautious of this distinction.

Tips for Accuracy

Repeat Measurements: Increase the reliability of your results by taking multiple measurements.

Understand Your Equipment: Know the limitations of your measurement tools and consider maximum error.