# 1.10 Calculating the capacitance of a capacitor.

Combining all of the factors we have considered, we can produce an equation, for calculating the capacitance of a capacitor.

C = ɛA/d.

• C is the capacitance measured in Farads.
• ɛ is the permittivity measured in Farads per metre.
• A is the cross sectional are between* the plates in metres squared.
• d is the separation of the plates in metres.

* Important, when we initially considered the effect of area in capacitance, we considered the area of the plates. As you can see in the equation above, it is actually the area between the two plates that affects the capacitance.

We seen that the field extending between the two plates of the capacitor, significantly enhances its ability to accumulate charge. This field can only extend between the plates, where they overlap each other and this is the area in which the charge accumulates. Therefore, it is the area between the plates, rather than their individual areas, that contributes to the capacitance