Absolute Error
Definition and meaning of Absolute Error in chemistry.
Absolute error is the exact numerical difference between a measured value and the true accepted value. It shows exactly how far a laboratory result lies from the correct target value. It is always reported using the exact same units as the original measurement.
In more detail
In any chemistry experiment, your measured results will almost never be perfectly exact. Absolute error helps you quantify exactly how far off your measurement is from perfection. You calculate absolute error by simply subtracting the true value from your measured experimental value.
The size of this absolute error directly indicates the overall accuracy of your laboratory measurement. A smaller absolute error means your measurement is highly accurate and very close to the truth. Because absolute error keeps the original chemical units, it has one major limitation.
It does not tell you if the error is actually significant relative to the whole sample. Missing a target by one gram is a huge deal if you are weighing two grams of powder. However, missing by one gram is completely meaningless if you are weighing a heavy shipping container.
To solve this problem, chemists also calculate relative error alongside the absolute error. Relative error expresses the exact same mistake as a helpful percentage of the total true value.
Key facts
| Mathematical definition | Measured value minus the true accepted value |
|---|---|
| Required units | Always the exact same as the original measurement |
| Primary purpose | Indicates the raw accuracy of a laboratory measurement |
| Sign meaning | A negative sign means the measurement was too low |
| Counterpart metric | Relative error (which uses percentages) |
| Field | Analytical chemistry and data analysis |
Suppose a student is testing a new electronic balance in the chemistry laboratory. The student places a standard calibration weight on the balance that has a true mass of 10.0 g. The electronic balance screen reads out a measured mass of exactly 9.8 g. To find the absolute error, the student subtracts 10.0 g from the measured 9.8 g. This simple calculation gives an absolute error of −0.2 g for the balance reading. The negative sign simply shows that the measured reading was lower than the actual true weight.
Frequently asked questions
How do you calculate the absolute error of a measurement?
You simply take your measured experimental value and subtract the known true value. The resulting number, including its positive or negative sign, is the absolute error.
What is the main difference between absolute error and relative error?
Absolute error is the plain numerical difference expressed in the original measurement units. Relative error takes that same mistake and expresses it as a percentage of the total true value.
Can absolute error be a negative number?
Yes, absolute error can absolutely be negative. A negative absolute error simply tells you that your measured laboratory value was lower than the accepted true value.