You can use our relative error calculator to estimate both the absolute and relative error for any measurement or calculation. Let's analyse the difference between these two types of error with an example.
Let's say you want to determine the value of the square root of two. The value you find online is 1.41421356237, but you wonder how accurate it would be to simply write it rounded to two significant figures. Note, that this is different to decimal points  see the significant figures calculator for more information.

To find out the absolute error, subtract the approximated value from the real one:
1.41421356237  1.41 = 0.00421356237

Divide this value by the real value to obtain the relative error:
0.00421356237 / 1.41421356237 = 0.298%
As you can see, the relative error is lower than 1%. In many cases, this is considered a good approximation.