How do you convert mega ohms to mega ohms.cm?

Sorry. You cannot convert ohm-cm to Mohms, just like you cannot convert mph to miles. They are two different concepts.

If you also have the thickness of the material (say along the z axis) in question, then you can divide ohm-cm by the thickness to get to ohm per square. In order to convert ohm per square to ohms, you also need to know the number of squares (the x-y plane).

An example. Let us assume a metal ruler of two cm wide (x), one meter long (y), and 0.2 cm thick (z). Let us assume the resistivity of the metal is 1 ohm-cm. Find the resistance of the metal along the length of the ruler (in the y direction).

Resistivity = 1 ohm-cm

Thickness = 0.2 cm.

Sheet resistance = 1 [ohm-cm] / 0.2 [cm] = 5 ohms/square

Number of squares = 1 [m] / 2 [cm] = 50 squares

Total resistance along y = Sheet resistance * number of squares = 250 ohms.

Q.E.D.

P.S. Note that the term, resistivity, is a general property of the metal, no specific design in mind. Resistance is calculated for a specific object (the ruler) made of the metal. "Square" is not one of the SI units, but "Square" and "sheet resistance" are terms used by engineers to describe thin films.

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