The discrepancy in measurements happens when **your object has been scaled in object mode, but the transformation has not been applied**.

As an example, look at this perfectly regular cube (2mx2mx2m) in **edit mode**:


[![enter image description here][1]][1]

What is wrong with it?


Look at the **scale** section on the panel in **object mode**:

[![enter image description here][2]][2]

If you select your object in **object mode** and press <kbd>Ctrl</kbd> <kbd>A</kbd> and select **Apply Scale**


[![enter image description here][3]][3]


The scale of the object will reset to 1,1,1

[![enter image description here][4]][4]

And the measurements in **edit mode** will reflect the real measurements of the object.

[![enter image description here][5]][5]


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Without applying transformations, you can also choose to display local or global measurements:

[![enter image description here][6]][6]

The measurements in **Local** units are **Relative to the Scale**, and show that the cube is 2x2x2, whereas the **Global** units show the **Absolute** measurements, revealing that the cube is no longer a cube, but a cuboid that is 4m tall and 2 meters wide.


[![enter image description here][7]][7]


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**Why should you care for local or global measurements?**
There are many operations that use the scale and rotation of the object and not its absolute dimensions (beveling, physics, UV unwrapping, physics simulations, etc)


Please read: https://blender.stackexchange.com/questions/7298/why-is-it-important-to-apply-transformation-to-an-objects-data

  [1]: https://i.sstatic.net/Awbg4.png
  [2]: https://i.sstatic.net/dDiZI.png
  [3]: https://i.sstatic.net/2gIIx.png
  [4]: https://i.sstatic.net/SCHaG.png
  [5]: https://i.sstatic.net/u5COQ.png
  [6]: https://i.sstatic.net/kjrjn.png
  [7]:https://i.sstatic.net/dIFWo.gif