Voltage
V = I × RLast updated:
Ohms Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law (V=IR). Essential electrical engineering tool with wattage and power factor calculations.
Ohm's Law Calculator
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Calculate voltage, current, resistance, and power
V = I × R
Ohm's Law
P = V × I
Power
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Electrical Engineering Foundation
Ohm\'s Law Calculator: Voltage, Current, Resistance & Power
Solve for any electrical quantity using V = IR and the power equations P = IV, P = I²R, P = V²/R.
Ohm's Law
V = I × R
Power (basic)
P = I × V
Power (current)
P = I²R
Power (voltage)
P = V²/R
Reviewed by: CalculatorApp Electrical Engineering Team
What Is Ohm\'s Law?
Ohm\'s Law is the fundamental relationship governing resistive electrical circuits. Proposed by Georg Simon Ohm in 1827, it establishes that the current through a conductor is directly proportional to voltage and inversely proportional to resistance. Combined with Kirchhoff\'s laws and the power equations, it forms the basis for all circuit design, safety calculation, and power engineering.
Current
I = V / RResistance
R = V / IPower (3 forms)
P=IV | P=I²R | P=V²/R| Resistor Type | Ohm\'s Law Applicability | Use Case |
|---|---|---|
| Fixed resistor | Full (linear) | Voltage dividers, current limiting |
| Semiconductor (diode) | Non-linear | Rectification, signal clamping |
| Inductor (AC) | Use Z = jωL | Filters, transformers, motors |
| Capacitor (AC) | Use Z = 1/jωC | Filters, timing, power factor correction |
History Timeline
1827: Georg Ohm publishes the mathematical relationship V = IR in Die galvanische Kette.
1845: Kirchhoff extends circuit theory with his voltage and current laws (KVL, KCL).
1861: British Association formalizes the ohm as the unit of resistance.
1881: International Congress of Electricians standardizes volt, ampere, and ohm globally.
1960: SI system formally adopts the ohm (Ω) as the unit of electrical resistance.
Modern era: Ohm's Law remains the entry point for all electrical engineering education and practice.
IEEE Xplore
Peer-reviewed electrical engineering research and standards.
IEC Standards
International electrotechnical safety and wiring standards.
NFPA NEC
US National Electrical Code for safe wiring practice.
OSHA Electrical
Workplace electrical safety regulations and guidelines.
Myth: Ohm's Law applies to all components.
Fact: Diodes, transistors, and other non-linear devices do not follow simple V = IR relationships.
Myth: Higher resistance always wastes more power.
Fact: P = V²/R — at constant voltage, higher resistance actually dissipates less power.
Myth: AC and DC obey Ohm's Law identically.
Fact: AC circuits with reactance require impedance Z; pure resistance circuits behave the same.
Myth: A circuit with low resistance is always safe.
Fact: Low resistance with high voltage = very high current = dangerous without proper protection.
FAQ (12)
What is Ohm's Law?
Ohm's Law states V = IR: voltage equals current multiplied by resistance. It is the cornerstone of circuit analysis.
Can I use Ohm's Law for AC circuits?
For resistive AC circuits, yes. For reactive components (inductors, capacitors), use impedance Z instead of R.
What is electrical power?
P = IV = I²R = V²/R. Power is the rate of energy dissipation in a resistor, measured in watts.
What are series and parallel rules?
Series: R_total = R₁ + R₂. Parallel: 1/R_total = 1/R₁ + 1/R₂. Voltage divides in series; current divides in parallel.
What is Kirchhoff's Voltage Law?
KVL: the sum of all voltage drops around any closed loop equals the sum of voltage rises (total = 0 net).
What is Kirchhoff's Current Law?
KCL: the sum of currents entering a node equals the sum leaving. Charge is conserved.
How is resistance related to material?
R = ρL/A where ρ is resistivity, L is length, and A is cross-sectional area.
What limits the accuracy of Ohm's Law?
Non-linear components (diodes, transistors) and extreme conditions (superconductors) do not follow simple V=IR.
What is a short circuit?
Near-zero resistance path causing very high current; potentially dangerous without overcurrent protection.
What is an open circuit?
Infinite resistance path; no current flows. Voltage may still appear across an open circuit.
How do I calculate current from power?
I = P / V or I = √(P/R). Use these forms when power and one other quantity are known.
What safety margin is standard in electrical design?
NEC and IEC standards typically require conductors rated at 125% of continuous load current for safety.
References
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