Greatest possible error calculator

The greatest possible error calculator below will find the error for you no matter how big the number you enter is. Enter a number followed by the unit.

However, leave a space between the number and the unit. This calculator will help you master the concept.

Greatest possible error

What is the greatest possible error (GPE)? No measurement is perfect. Whenever you are doing some measurement, there is a great likelihood that it is not exact.

Definition: The greatest possible error in a measurement is half of the measuring unit.

For example, what is the greatest possible error for 8 cm?

8 cm was measured to the nearest 1 cm, so the measuring unit is 1 cm.  The greatest possible error is 0.5 times 1 or 0.5 cm.

What is the GPE for 4.2 inches?

This time 4.2 was measured to the nearest tenth of an inch or 0.1 inch, so the measuring unit is 0.1. The GPE is 0.5 times 0.1 inch or 0.05 inch.

Real life application of the greatest possible error

You measure a garden that is rectangular as shown in the diagram. Find the minimum and maximum area of the garden. 

The measurements were made to the nearest foot, so the greatest possible error is 0.5 foot.

The width of the garden could be as little as 27 - 0.5 = 26.5 or as big as 27 + 0.5 = 27.5

The length of the garden could be as little as 18 - 0.5 = 17.5 or as big as 18 + 0.5 = 18.5

The minimum area = 26.5 × 17.5 = 463.75 square feet

The maximum area = 27.5 × 18.5 = 508.75 square feet

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