Ohm’s law & power calculator
Enter a voltage and a resistance to get the current and the power instantly. Ohm’s law says V = IR, so the current is I = V/R. Electrical power can be written three equivalent ways: P = VI = I²R = V²/R. For example, 12 V across 100 Ω drives 0.12 A and transfers 1.44 W.
What if you changed…
Double the voltage. What happens to current? What happens to power?
See the calculation
- I = V/R = 12/100 = 0.12 A.
- P = VI = 12 × 0.12 = 1.44 W.
What this model assumes
Ideal DC voltage source and an ohmic resistor with constant resistance; wires have zero resistance.
Keep an eye on this
Real components have power ratings and may heat up; this educational model is not a circuit safety check.
Understand the physics ↗Formulas used in this simulation
- Ohm’s law
- V = IR
- Voltage = current × resistance
- Current
- I = V/R
- Amperes from volts and ohms
- Resistance
- R = V/I
- Ohms from a measurement
- Power
- P = VI
- Watts = volts × amperes
- Power from current
- P = I²R
- Substitute V = IR
- Power from voltage
- P = V²/R
- Substitute I = V/R
Ohm’s law & power: common questions
Wondering about the why? Start here.
What is the Ohm’s law power formula?
Combine P = VI with V = IR to get P = I²R, or with I = V/R to get P = V²/R. All three give the same power for an ohmic resistor.
If the voltage doubles, what happens to the power?
At constant resistance the current doubles and the power increases fourfold, because P = V²/R.
What units does Ohm’s law use?
Voltage in volts (V), current in amperes (A), resistance in ohms (Ω) and power in watts (W). Convert milliamps and kilohms before substituting.
What happens when resistance increases?
At fixed voltage, current decreases because I = V/R. Power also decreases as V²/R.
Why is zero resistance not allowed?
An ideal source connected across zero resistance would demand an unbounded current. Real circuits have internal resistance and other limits.