Can Ohm's Law be used for AC?

For pure resistive loads, yes. For reactive circuits, use impedance: V = I × Z.

What is an Ohm's Law example?

12V battery with 4Ω resistor: I = 12/4 = 3 amps current flow.

⚡ Ohm's Law Calculator 2026

Q: What is Ohm's Law formula?

V = I × R, where V is voltage, I is current, R is resistance. Rearranged: I = V/R, R = V/I.

Q: How do I calculate voltage?

V = I × R. Multiply current (amps) by resistance (ohms). Example: 2A × 10Ω = 20V.

Q: How do I calculate resistance?

R = V / I. Divide voltage by current. Example: 12V ÷ 2A = 6Ω.

Q: What is the power formula?

P = V × I, P = I² × R, or P = V² / R. All give power in watts.

Q: How do I convert ohms to watts?

Use P = V²/R (with voltage) or P = I²×R (with current).

Q: What is the Ohm's Law triangle?

Memory aid with V at top, I and R at bottom. Cover the unknown to see the formula.

Q: What are Ohm's Law units?

Voltage in volts (V), current in amps (A), resistance in ohms (Ω), power in watts (W).

Q: Why is Ohm's Law important?

Fundamental to electrical engineering for designing circuits, calculating power, and troubleshooting.

Calculate Voltage (V), Current (I), Resistance (R) & Power (P) — Enter any 2 values

Enter any 2 known values and click Calculate. Leave unknown fields empty.

🔌 Voltage (V/E)

⚡ Current (I)

Ω Resistance (R)

💡 Power (P)

💡 Tip: V = I × R (Ohm's Law). P = V × I (Watt's Law). From these, all 12 formulas derive!

Ohm's Law Formula Wheel

VI×R
P/I
√(P×R)

IV/R
P/V
√(P/R)

PV×I
I²×R
V²/R

RV/I
P/I²
V²/P

All Ohm's Law Formulas

Find	Formula 1	Formula 2	Formula 3
Voltage (V)	`V = I × R`	`V = P / I`	`V = √(P × R)`
Current (I)	`I = V / R`	`I = P / V`	`I = √(P / R)`
Resistance (R)	`R = V / I`	`R = P / I²`	`R = V² / P`
Power (P)	`P = V × I`	`P = I² × R`	`P = V² / R`

Understanding Ohm's Law

⚡ What is Ohm's Law?

Ohm's Law states that current (I) flowing through a conductor is directly proportional to voltage (V) and inversely proportional to resistance (R). Formula: V = I × R.

💡 Watt's Law (Power)

Watt's Law relates power to voltage and current: P = V × I. Combined with Ohm's Law, this gives us all 12 electrical formulas for any calculation.

🔺 The Ohms Triangle

The Ohms Law Triangle (V-I-R) helps remember formulas. Cover the unknown: V on top, I and R on bottom. V=IR, I=V/R, R=V/I.

🌐 AC vs DC Circuits

For DC circuits, use basic Ohm's Law. For AC circuits, resistance becomes impedance (Z): V = I × Z. Impedance includes capacitive and inductive reactance.

Frequently Asked Questions

What is Ohm's Law formula?

The Ohm's Law formula is V = I × R, where V is voltage (volts), I is current (amps), and R is resistance (ohms). Rearranged: I = V/R and R = V/I. This is the foundation of electrical circuit calculations.

How do I calculate voltage from current and resistance?

Use V = I × R. Multiply current (in amps) by resistance (in ohms). Example: 2A × 10Ω = 20V. This is the basic Ohm's Law equation for finding voltage.

How do I calculate resistance from voltage and current?

Use R = V / I. Divide voltage by current. Example: 12V ÷ 2A = 6Ω. This resistance formula is derived directly from Ohm's Law.

How do I calculate current from voltage and resistance?

Use I = V / R. Divide voltage by resistance. Example: 120V ÷ 60Ω = 2A. This tells you how much current flows through a circuit.

What is the power formula in Ohm's Law?

Power formulas: P = V × I (voltage × current), P = I² × R (current squared × resistance), P = V² / R (voltage squared ÷ resistance). All give power in watts.

How do I convert ohms to watts?

You need voltage or current plus resistance. P = V²/R (with voltage) or P = I²×R (with current). Example: 120V across 60Ω = 14,400/60 = 240 watts.

How do I convert amps to ohms?

You need voltage. Use R = V / I. Example: 12V with 2A = 12/2 = 6 ohms. You cannot convert amps to ohms directly without knowing voltage.

What is the Ohm's Law triangle?

The Ohms Law triangle is a memory aid with V at top, I and R at bottom. Cover the unknown value: V = I×R (I and R visible, multiply), I = V/R, R = V/I (V over the other, divide).

What is the Ohm's Law formula wheel?

The formula wheel shows all 12 formulas arranged in a circle. Divided into 4 sections (V, I, R, P), each shows 3 formulas to calculate that value from any two known values.

Can I use Ohm's Law for AC circuits?

For pure resistive AC loads, yes. For circuits with capacitors/inductors, replace R with impedance (Z): V = I × Z. Impedance includes reactance and is measured in ohms.

What is 3-phase Ohm's Law calculation?

For 3-phase circuits: P = √3 × V × I × pf (power factor). Line voltage = √3 × phase voltage. Ohm's Law applies per phase, but total power calculation differs from single phase.

What units does Ohm's Law use?

Standard SI units: Voltage in volts (V), Current in amps (A), Resistance in ohms (Ω), Power in watts (W). Convert milli/kilo prefixes before calculating.

What are Ohm's Law examples?

Example 1: 12V battery, 4Ω resistor → I = 12/4 = 3A. Example 2: 5A through 10Ω → V = 5×10 = 50V. Example 3: 100W at 20V → I = 100/20 = 5A.

Why is Ohm's Law important?

Ohm's Law is fundamental to all electrical engineering. It helps design circuits, select components, calculate power consumption, ensure safety, and troubleshoot electrical problems. Every electrician uses it daily.

What is relationship between voltage, current, resistance?

Voltage "pushes" current through resistance. Higher voltage = more current (if R constant). Higher resistance = less current (if V constant). V, I, and R are interdependent per V = I × R.

What resistor do I need for an LED?

Use R = (Vsupply - Vled) / Iled. Example: 5V supply, 2V LED, 20mA → R = (5-2)/0.02 = 150Ω. Then calculate power: P = I²×R = 0.02²×150 = 0.06W, so use ¼W resistor.

How accurate is this Ohm's Law calculator?

Uses JavaScript double-precision (64-bit) floating-point for ~15-16 significant digits. For practical electrical work, this far exceeds component tolerances (typically 1-10%).