1. The current flowing through the device (I): This is the amount of electrical charge passing through the device per unit of time. It's measured in amperes (A).

2. The resistance of the device (R): This is a measure of how much the device opposes the flow of electrical current. It's measured in ohms (Ω).

Once you have these two values, you can use Ohm's Law to calculate the voltage (V):

V = I * R

Where:

* V is the voltage in volts (V)

* I is the current in amperes (A)

* R is the resistance in ohms (Ω)

Example:

If a device has a resistance of 10 ohms and a current of 2 amperes flowing through it, the voltage across the device would be:

V = 2 A * 10 Ω = 20 V

Note:

* You can also use other methods to determine the voltage across a device, such as using a voltmeter or analyzing the circuit's configuration and power sources.

* The formula above assumes a direct current (DC) circuit. For alternating current (AC) circuits, the calculations are more complex and require consideration of the phase angle and other factors.