Percent ErrorHow to Calculate it.

ERROR!

Error = Measured Value – Accepted Value

• Science references list the density of aluminum as being 2.7g/cm3.

• Suppose you perform an experiment and your results show aluminum having a density of 2.8g/cm3

Aluminum 2.7g/cm3

Aluminum 2.8g/cm3

Accepted

Measured

Error = 2.8g/cm3 – 2.7g/cm3 = 0.1g/cm3

Error can be positive or negative but sometimes it isn’t very useful!

• If you have a 10ft long table (accepted value) and your results state it is 5ft long (measured value) your error is 5ft.

• Goal line to Goal line, a football field is 300 feet (known value). If you measure its length and come up with 290ft your error is 10ft.

• Even though the first measurement was off by only 5ft, the second measurement which is off by 10ft is much better.

• In terms of percentages, the first measurement was off by 50% of the value whereas the second was only off by 3.3%.

Error is 5ft out of 10

Error is 10ft but out of 300ft

You can have an error of a million miles if you were measuring the distance to the sun but it would only be a 1-2% error because the sun is 93 million miles away!

• Aluminum has an accepted value of 2.7g/cm3.Suppose you perform an experiment and your results show aluminum as having a density of 2.8g/cm3. What is your percent error?

Get a difference.

Compare to Accepted value.

Multiply by 100.

A student measured the temperature of boiling water and got an experimental reading of 97.5°C. Calculate the % error.

Get a difference.

Compare to Accepted value.

Multiply by 100.