What is Ohm's Law formula?

Ohm's Law is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. Rearranged, it gives I = V ÷ R and R = V ÷ I. Combined with the power formula P = V × I, these four equations let you solve any DC resistive circuit.

How do I calculate voltage from current and resistance?

Multiply current by resistance: V = I × R. For example, 0.5 A flowing through a 100 Ω resistor produces a voltage drop of 0.5 × 100 = 50 V across the resistor.

What is the Ohm's Law triangle?

The Ohm's Law triangle is a memory aid with V on top and I and R on the bottom. Cover the variable you want to find: V (uncovered I × R), I (uncovered V ÷ R), or R (uncovered V ÷ I). The Ohm's Law wheel extends this with the power formulas so you can also solve for P.

How do I calculate power from voltage and current?

Multiply voltage by current: P = V × I. A 120 V appliance drawing 5 A consumes 120 × 5 = 600 W. If you know the resistance instead, use P = I² × R or P = V² ÷ R.

Does Ohm's Law apply to AC circuits?

It applies to purely resistive AC loads (heaters, incandescent bulbs). For circuits with capacitors or inductors, replace resistance with impedance (Z) and use RMS values. Real AC power also requires the power factor: P = V_rms × I_rms × cos(φ).

Ohm's Law Calculator

Ohm's Law is the fundamental relationship between voltage, current, and resistance in an electrical circuit: V = I × R. Combined with the power equation P = V × I, it forms the Ohm's Law wheel — a set of twelve formulas that let you solve for any one of V, I, R, or P given any two of the others. This calculator uses an interactive wheel visualization: pick the value you want to calculate, enter the two you know, and get instant results along with the derived power dissipation. It is the workhorse formula behind every resistor, LED, heater, motor, and power supply design.

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calendar_today Updated: April 2026

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Formula Used

V = I × R

Calculated Result

12 V

Voltage

All Values

bolt Voltage

12 V

electric_bolt Current

2 A

memory Resistance

6 Ω

Power Dissipation

24 W

offline_bolt

P = V × I = 12 × 2

Ohm's Law Formulas

Voltage

V = I×R

Current

I = V/R

Resistance

R = V/I

Input Values

Solve For

Voltage (V = I × R)

Current (I = V ÷ R)

Resistance (R = V ÷ I)

Voltage (V)

Current (A)

Resistance (Ω)

electric_bolt Common Voltages

USB 5V DC

Car Battery 12V DC

US Outlet 120V AC

EU Outlet 230V AC

lightbulb Quick Tips

⚡ V = I × R (Voltage = Current × Resistance)
🔌 P = V × I (Power = Voltage × Current)
⚠️ Higher voltage = more dangerous

science 12V car accessory with 6Ω resistance

Using I = V ÷ R, current = 12 ÷ 6 = 2 A. Power dissipated is P = V × I = 12 × 2 = 24 W. This tells you the load draws 2 amps and dissipates 24 watts of heat — important for choosing wire gauge and verifying the resistor's power rating.

Expected Results

How to Use This Calculator

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Pick What to Calculate

Click Voltage, Current, or Resistance on the Ohm's Law wheel (or the buttons below it) to choose which variable to solve for.

edit

Enter the Two Known Values

Fields for the other two variables appear. Type the values you already know — for example, enter current (A) and resistance (Ω) to find voltage (V).

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Read Instant Results

The calculated value updates live, along with the power dissipation (P = V × I) and the exact formula used.

The Formula

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points, with resistance as the constant of proportionality. Power is the rate at which electrical energy is converted to heat, light, or mechanical work. Together these give a family of twelve formulas covering every pair of knowns.

V = I × R | I = V ÷ R | R = V ÷ I | P = V × I = I² × R = V² ÷ R

lightbulb Variables Explained

V Voltage (volts, V) — electrical potential difference
I Current (amperes, A) — rate of charge flow
R Resistance (ohms, Ω) — opposition to current flow
P Power (watts, W) — rate of energy transfer

tips_and_updates Pro Tips

Always check the power rating of resistors: a resistor that passes the right current may still burn out if P exceeds its watt rating (common values: 1/4 W, 1/2 W, 1 W).

For LEDs, use a series resistor: R = (V_supply − V_LED) ÷ I_LED. A 5V supply and 2V / 20mA LED needs (5 − 2) ÷ 0.02 = 150 Ω.

Use milliamps (mA) and milliwatts (mW) for small circuits: 1 A = 1000 mA, 1 W = 1000 mW. The math is identical.

Ohm's Law is strictly true only for ohmic (linear) materials. Diodes, LEDs, and semiconductors do NOT follow V = IR directly.

For AC circuits with reactive loads, replace R with impedance (Z) and include the power factor: P = V × I × cos(φ).

Frequently Asked Questions

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Ohm's Law Calculator

All Values

Ohm's Law Formulas

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science 12V car accessory with 6Ω resistance

Expected Results

How to Use This Calculator

Pick What to Calculate

Enter the Two Known Values

Read Instant Results

The Formula

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Frequently Asked Questions

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