${\displaystyle U_{\text{ab}}={\displaystyle \underset{r_{\text{a}}}{\overset{r_{\text{b}}}{\int }}E\cdot \text{d}r}}$

where r_a and r_b are the position vectors for a and b, respectively, and dr is the vector line element

NOTE 1 – In the case of an irrotational field strength, the voltage is independent of the path and equal to the negative of the electric potential difference between the two points:

${\displaystyle U_{\text{ab}}=-\left(V_{\text{b}}-V_{\text{a}}\right)}$

NOTE 2 – The name "voltage", commonly used in the English language, is an exception from the principle that a quantity name should not refer to any name of unit.