## Calculating the moment of inertia (I)

For simple shapes such as squares, rectangles and circles, simple formulas have been worked out and the values must be calculated for each case.

Because millimetres are used, large numbers are generated in the calculation.

A standard method of denoting moment of inertia is to write the values as: number x 10^{6}10^{6} is a compact way of writing 1,000,000 or 1 million. mm^{4}.

The 10^{6} factor removes unwanted digits from the value.

The calculation is usually worked using four significant figures The **number of significant figures** is the number of digits used to represent the original number once it has been rounded to the given number of digits, eg 25.0658 is written as 25.07 when rounded to four significant digits. , so some rounding off is required and the decimal point may need to be moved to use the factor of 10^{6}.

Example: 73,473,278 mm^{4} is written as 73.47 x 10^{6} mm^{}^{4}