Engineering · Electrical
Ohm's Law Calculator — Voltage, Current, Resistance & Power
Solve Ohm's law (V = I × R) and the power law (P = V × I) from any two known values — voltage, current, resistance or power — with SI prefixes (mA, kΩ, kW…) and every formula shown. Handy for resistors, LEDs, heaters, fuses and appliance currents.
Your inputs
Quick start — try a typical case
Your result Live
Resistance and Power
46 Ω · 1.15 kW
- Voltage (V)
- 230 V (given)
- Current (I)
- 5 A (given)
- Resistance (R)
- 46 Ω — R = V ÷ I
- Power (P)
- 1.15 kW — P = V × I
Working
1: Step 1 · Resistance
R = V ÷ I
Expression becomes 46 Ω
2: Step 2 · Power
P = V × I
Expression becomes 1.15 kW
These relationships hold for resistive loads and DC circuits; for AC motors and electronics, power factor makes the real power lower than V × I.
How this is calculated
V = I × R · P = V × I = I² × R = V² ÷ R
- V
- Voltage in volts
- I
- Current in amperes
- R
- Resistance in ohms
- P
- Power in watts
Ohm's law links voltage, current and resistance: the current through a resistor is the voltage across it divided by its resistance. Combined with P = V × I, any two of the four quantities determine the other two.
Assumptions & sources
- Resistive (ohmic) loads; DC or AC with unity power factor.
- 1The International System of Units (SI) — derived units: volt, ampere, ohm, watt — BIPM
- 2Physics, Class 10 — Electricity (Ohm's law, electric power) — NCERT
Calculator ID ENG-OHM-001 · version 1.0.0
Common questions
How many amps does a 1,500 W heater draw on 230 V?
I = P ÷ V = 1,500 ÷ 230 ≈ 6.5 A.
What resistor do I need for an LED?
R = (supply voltage − LED forward voltage) ÷ LED current. For 5 V, a 2 V LED and 20 mA: (5 − 2) ÷ 0.02 = 150 Ω.