VoltBasePRO
Electrical Reference
Electrical FundamentalsNo sign-up • Shows its working

Resistance Calculator

Calculate resistance in Ohms (Ω) from voltage and current, voltage and power, or power and current.

1. Enter your numbers  →  2. Check the answer  →  3. Read the steps before you trust it

V
A

Calculated Resistance

Resistance (R)
24Ω
Power (P)
600W

Step-by-Step Engineering Calculation

  1. 1Formula: R=VIR = \frac{V}{I}
  2. 2R=120 V5 A=24.00 ΩR = \frac{120\text{ V}}{5\text{ A}} = \mathbf{24.00\ \Omega}
  3. 3Power: P=V×I=120 V×5 A=600 WP = V \times I = 120\text{ V} \times 5\text{ A} = \mathbf{600\text{ W}}

Formula & Theory

R = V / I | R = V² / P | R = P / I²

Computes resistance in Ohms describing how strongly a component opposes electric current.

Variable Definitions
R:
Resistance (Ohms (Ω)) – Electrical resistance
V:
Voltage (Volts (V)) – Applied voltage
I:
Current (Amperes (A)) – Circuit current

Worked Engineering Example

Heating Element Resistance

A 240V water heater element rated for 4500W.

Inputs:
  • Voltage: 240 V
  • Power: 4500 W
Result: Resistance = 12.80 Ω, Current = 18.75 A

Key Assumptions

  • •Element at operating temperature.

Limitations & Safety Scope

  • •Cold resistance of tungsten filaments or heating alloys can be significantly lower than hot operating resistance.

Frequently Asked Questions

Why does resistance change with temperature?

Conductor metals have positive temperature coefficients; atomic thermal vibrations increase electron scattering at higher temperatures.

Related Calculators & Engineering Tools

Resistor Series/Parallel Calculator
Resistor Color Code Calculator

Educational & Reference Notice: This calculator provides technical estimates based on standard physical formulas. Actual electrical installation, protective device sizing, and conductor selection must be verified against the applicable electrical code (NEC, IEC, CEC) by a licensed electrician or qualified professional engineer.