The main thing to keep in mind, is the base unit must be the same for each measurement. For example,
when calculating the area of a rectangle and you measure the length and width in inches then the area
will be in square inches.
It doesn't matter what the measurement unit is as long as all measurements use it. If you measure
in centimeters then the area will be square centimeters. If you measure in miles then the area will
be square miles. etc.
If you measure the length in inches and the width in feet, the result will be incorrect. Make sure
to first convert all measurements to the same base unit before using the calculator.
Once you have the area of the shape in square form, you can then easily convert that to whatever
unit you need on the area conversion page.
The radius is not the diameter
Another common mistake is entering the diameter of a shape when the radius is asked for.
The radius is 1/2 the diameter. So if you only know the diameter, be sure to divide by 2 to determine