How to convert ohms to volts

How to convert electric resistance in ohms (Ω) to electrical voltage in volts (V).

You can calculate volts from ohms and amps or watts, but you can't convert ohms to volts since ohm and volt units do not measure the same quantity.

Ohms to volts calculation with amps

According to ohm's law, the voltage V in volts (V) is equal to the current I in amps (A) times the resistance R in ohms (Ω):

V(V) = I(A) × R(Ω)

So volts are equal to amps times ohms:

volts = amps × ohms

or

V = A × Ω

Example

Calculate the voltage in volts when resistance is 25 ohms and the current is 0.2 amps.

The voltage V is equal to 0.2 amps times 25 ohms, which is equal to 5 volts:

V = 0.2A × 25Ω = 5V

Ohms to volts calculation with watts

The power P is equal to the voltage V times the current I:

P = V × I

The current I is equal to the voltage V divided by the resistance R (ohm's law):

I = V / R

So the power P is equal to

P = V × V / R = V 2 / R

So the voltage V in volts (V) is equal to the square root of the power P in watts (W) times the resistance R in ohms (Ω):

                    __________________

V(V) = √P(W) × R(Ω)

So volts are equal to the square root of watts times ohms:

volts = √watts × ohms

or

V = √W × Ω

Example

Calculate the voltage V in volts when the resistance is 12.5Ω and the power is 2 watts.

The voltage V is equal to the square root of 2 watts times 12.5 ohms, which is equal to 5 volts:

V = √2W × 12.5Ω = 5V

How to convert volts to ohms »

What is Ohm's law?

Ohm's Law is a formula used to calculate the relationship between voltage, current and resistance in an electrical circuit.

To students of electronics, Ohm's Law (E = IR) is as fundamentally important as Einstein's Relativity equation (E = mc²) is to physicists.

E = I x R

When spelled out, it means voltage = current x resistance, or volts = amps x ohms, or V = A x Ω.

Named for German physicist Georg Ohm (1789-1854), Ohm's Law addresses the key quantities at work in circuits:

QuantityOhm's Law
symbol
Unit of measure
(abbreviation)
Role in circuitsIn case you're wondering:
VoltageEVolt (V)Pressure that triggers electron flowE = electromotive force (old-school term)
CurrentIAmpere, amp (A)Rate of electron flowI = intensity
ResistanceROhm (Ω)Flow inhibitorΩ = Greek letter omega

If two of these values are known, technicians can reconfigure Ohm's Law to calculate the third. Just modify the pyramid as follows:

If you know voltage (E) and current (I) and want to know resistance (R), X-out the R in the pyramid and calculate the remaining equation (see the first, or far left, pyramid above).

Note: Resistance cannot be measured in an operating circuit, so Ohm's Law is especially useful when it needs to be calculated. Rather than shutting off the circuit to measure resistance, a technician can determine R using the above variation of Ohm's Law.

Now, if you know voltage (E) and resistance (R) and want to know current (I), X-out the I and calculate the remaining two symbols (see the middle pyramid above).

And if you know current (I) and resistance (R) and want to know voltage (E), multiply the bottom halves of the pyramid (see the third, or far right, pyramid above).

Try a few sample calculations based on a simple series circuit, which includes just one source of voltage (battery) and resistance (light). Two values are known in each example. Use Ohm's Law to calculate the third.


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