Ohm’s Law Calculator
Calculate electrical voltage, current, resistance, or power using Ohm’s Law. Enter any two known values to find the other two. For example, enter voltage and wattage to find the current and resistance.
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How to Use Ohm’s Law to Find Voltage, Current, Resistance, or Power
Ohm’s Law defines the relationship between electric current, resistance, and voltage. More specifically,
“Ohm’s law states that the current through a conductor between two points is directly proportional to the potential difference across the two points.” (Wikipedia).
Ohm’s Law and the calculator above can be used to find voltage, current, power, and resistance if at least two of the values are known. For example, if voltage and resistance is known, then the calculator will find power and current. Alternatively, the power and resistance can be solved if the voltage and current is known.
Ohm’s Law provides the equation I = E ÷ R, where I is the current through a conductor measured in amperes, V is the potential difference across the conductor measured in volts, and R is the resistance of a conductor measured in ohms.
Current(I) = Voltage(E) ÷ Resistance(R)
Ohm’s Law Triangle
The Ohm’s Law triangle can help solve all of the Ohm’s law formulas to find voltage, current, or resistance. To use the triangle, cover the value being solved for and use the remaining two values to calculate it.
For example, to find the voltage, cover the E in the triangle, which leaves I and R are next to each other. This shows that the equations to solve voltage is I × R (current × resistance).
Alternatively, to solve for current, cover the I in the triangle, which leaves E ÷ R, expressed as the voltage divided by the resistance.
Watt’s Law states that electric power measured in watts is equal to the of the circuit current times the voltage. This formula is very similar to Ohm’s law and can help solve for power/wattage.
Watt’s Law is often used in conjunction with Ohm’s Law to solve electrical properties when the power of the circuit is known.
Power(P) = Current(I) × Voltage(E)
Our watts to amps calculator uses this formula to convert between power and current in electrical circuits, for example.
Ohm’s Law Formulas to Solve Voltage, Power, Current, and Resistance
Ohm’s Law can be used to find volts, watts, amps, or ohms if any two values are known. This can be done using the Ohm’s Law and Watt’s Law formulas above. Refer to this diagram to see all of the formulas used to find volts, watts, amps, or ohms.
Formulas to Calculate Volts
These three formulas can be used to solve for voltage.
Voltage = Current × Resistance
Voltage = Power ÷ Current
Voltage = Power × Resistance
Formulas to Calculate Watts
Use these formulas to solve for power.
Power = Voltage × Current
Power = Voltage2 ÷ Resistance
Power = Current2 × Resistance
Formulas to Calculate Amps
These three formulas can be used to solve for current.
Current = Voltage ÷ Resistance
Current = Power ÷ Voltage
Current = Power ÷ Resistance
Formulas to Calculate Ohms
These formulas that can be used to solve for resistance.
Resistance = Voltage ÷ Current
Resistance = Voltage2 ÷ Power
Resistance = Power ÷ Current2
Ohm’s Law is used for many things, from understanding how large of a microwave can be used without blowing a circuit breaker to knowing how many light fixtures can be safely installed on a circuit without creating a fire hazard.
Use Ohm’s Law to help size an electrical circuit or find out how large of a heater can be safely used on a regular outlet. You might also find our voltage drop calculator to determine voltage drop, the minimum wire size needed, and the maximum wire length for your next electrical project.