Ohm's Law Resistance Calculator
Calculate electrical resistance using Ohm's law formulas with voltage, current, and power
Ohm's Law Resistance Calculations
Electrical potential difference in volts
Electric current in amperes
Resistance Calculation Results
Resistance Analysis
Resistance Calculation Formulas
Primary Formula
R = V/I
Most common formula using voltage and current
Power-Based Formulas
R = V²/P (voltage & power)
R = P/I² (current & power)
Basic Ohm's Law
V = I × R
I = V/R
P = V × I
Resistance Units & Prefixes
Ohm (Ω)
Basic unit of electrical resistance
Kiloohm (kΩ)
1,000 ohms
Megaohm (MΩ)
1,000,000 ohms
Milliohm (mΩ)
0.001 ohms
Resistance Tips
Higher resistance = less current flow
Resistance depends on material, length, and cross-sectional area
Temperature affects resistance in most materials
Use appropriate wire gauge to minimize resistance losses
Understanding Electrical Resistance and Ohm's Law
What is Electrical Resistance?
Electrical resistance is a measure of how much a material opposes the flow of electric current. It's an intrinsic property that depends on the material's composition, temperature, length, and cross-sectional area. Resistance is measured in ohms (Ω).
Ohm's Law for Resistance
Georg Ohm discovered that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. This relationship gives us the fundamental formula R = V/I.
Factors Affecting Resistance
- •Material: Conductors (copper), semiconductors (silicon), insulators (rubber)
- •Length: Longer conductors have higher resistance
- •Cross-sectional area: Thicker conductors have lower resistance
- •Temperature: Typically increases resistance in metals
Resistance Formula Applications
R = V/I
Primary formula when voltage and current are measured. Most commonly used in circuit analysis and troubleshooting.
R = V²/P
Useful when you know the voltage rating and power consumption of a device. Common for calculating resistor values.
R = P/I²
Applied when power and current are known. Useful for power dissipation calculations.
Remember: Resistance is constant for linear components at a given temperature, but can vary with voltage in non-linear components.
Real-World Resistance Examples
Household Wiring
12 AWG copper wire: ~0.002 Ω per foot
Low resistance for efficient power transmission
LED Current Limiting
330Ω resistor for 20mA LED at 5V
R = (5V - 2V) ÷ 0.02A = 150Ω minimum
Heating Element
1500W heater at 120V: 9.6Ω
R = V²/P = (120)² ÷ 1500 = 9.6Ω
Resistance in Different Circuit Configurations
Series Resistance
Rtotal = R₁ + R₂ + R₃ + ...
Resistances add directly. Current is the same through all resistors.
Parallel Resistance
1/Rtotal = 1/R₁ + 1/R₂ + 1/R₃ + ...
Total resistance is less than the smallest individual resistance.