Resistance Calculator
Calculate electrical resistance using Ohm's Law, series and parallel resistor networks, or from material resistivity and wire dimensions. Essential for engineers, students, and electronics enthusiasts.
What Is Electrical Resistance?
Electrical resistance is a measure of the opposition to the flow of electric current through a conductor. It is measured in ohms (Ω). Resistance depends on the material, its dimensions, and temperature. According to Ohm's Law, resistance is the ratio of voltage to current: R = V / I.
This calculator supports four modes:
- Ohm's Law: Calculate resistance from voltage and current, or voltage from resistance and current.
- Series: Calculate the total resistance of resistors connected in series.
- Parallel: Calculate the total resistance of resistors connected in parallel.
- Resistivity: Calculate resistance from material resistivity, wire length, and cross-sectional area.
How Does the Resistance Calculator Work?
The calculator uses the following formulas:
Ohm's Law: R = V / I
Series: Rtotal = R₁ + R₂ + R₃ + ... + Rn
Parallel: 1/Rtotal = 1/R₁ + 1/R₂ + 1/R₃ + ... + 1/Rn
Resistivity: R = ρ × L / A
Where: ρ = resistivity (Ω·m), L = length (m), A = cross-sectional area (m²)
Power: P = V × I = I² × R = V² / R
For series and parallel modes, you can add or remove resistors dynamically. Each resistor value is entered in ohms (Ω).
Why Use This Resistance Calculator?
- Four Modes: Ohm's Law, series, parallel, and resistivity calculations.
- Dynamic Resistor Arrays: Add or remove resistors for series and parallel circuits.
- Material Presets: Choose from common conductor materials with preset resistivity values.
- Step-by-Step: See the calculation steps for better understanding.
- Free & Private: No registration, no data storage.
❓ Resistance Calculator FAQ
What is Ohm's Law?
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points. The formula is V = I × R, where V is voltage, I is current, and R is resistance.
How do I calculate total resistance in series?
For resistors in series, simply add all the resistance values together: Rtotal = R₁ + R₂ + R₃ + ...
How do I calculate total resistance in parallel?
For resistors in parallel, use the reciprocal formula: 1/Rtotal = 1/R₁ + 1/R₂ + 1/R₃ + ...
What is resistivity?
Resistivity (ρ) is a material property that measures how strongly a material opposes the flow of electric current. It is measured in ohm-meters (Ω·m). Materials with low resistivity (like copper and silver) are good conductors.
What is the resistivity of copper?
The resistivity of copper is approximately 1.68 × 10⁻⁸ Ω·m at 20°C. This makes it one of the best conductors for electrical wiring.
What is the difference between resistance and resistivity?
Resistance (R) depends on the material, length, and cross-sectional area of a specific conductor. Resistivity (ρ) is a material property that is independent of the conductor's dimensions. R = ρ × L / A.
How does temperature affect resistance?
For most conductors, resistance increases with temperature. This is because higher temperature causes more atomic vibrations, which impede the flow of electrons. Some materials (like semiconductors) have a negative temperature coefficient.
What is the unit of resistance?
Resistance is measured in ohms (Ω). One ohm is the resistance that allows one ampere of current to flow when one volt of potential is applied.
What is the difference between series and parallel circuits?
In a series circuit, components are connected end-to-end, and the same current flows through all components. In a parallel circuit, components are connected across the same two points, and the voltage is the same across all components.
How do I calculate voltage from resistance and current?
Use Ohm's Law: V = I × R. Multiply the current (in amperes) by the resistance (in ohms) to get the voltage (in volts).
How do I calculate current from voltage and resistance?
Use Ohm's Law: I = V / R. Divide the voltage (in volts) by the resistance (in ohms) to get the current (in amperes).
What is the resistivity of aluminum?
The resistivity of aluminum is approximately 2.82 × 10⁻⁸ Ω·m at 20°C. Aluminum is commonly used in overhead power lines because it is lightweight and has good conductivity.
What is the SI unit of resistivity?
The SI unit of resistivity is ohm-meter (Ω·m). It is often expressed in µΩ·cm or nΩ·m for convenience.
How do I calculate power from resistance and current?
Power (P) = I² × R. Square the current (in amperes) and multiply by the resistance (in ohms) to get power in watts.
What is the formula for resistance of a wire?
The resistance of a wire is given by R = ρ × L / A, where ρ is resistivity, L is length, and A is the cross-sectional area.
Can this calculator handle more than 3 resistors?
Yes. In series and parallel modes, you can add as many resistors as you need by clicking the "Add Resistor" button. The calculator will automatically update the total resistance.
What is the resistivity of nichrome?
Nichrome (an alloy of nickel and chromium) has a resistivity of about 100 × 10⁻⁸ Ω·m, making it a poor conductor but excellent for heating elements.