Ohm's Law Calculator — Voltage, Current & Resistance (V = I × R)V = I×R · I = V/R · R = V/I · Volts · Amps · Ohms (Ω)
Use this free Ohm's Law Calculator to instantly solve any unknown variable in the fundamental Ohm's Law equation — V = I × R — the cornerstone of all electrical circuit analysis. Enter any two known electrical values to automatically solve the third: Voltage (V = I × R) in Volts (V) · Current (I = V / R) in Amperes (A) or milliamps (mA) · Resistance (R = V / I) in Ohms (Ω), kΩ, or MΩ — with automatic unit conversion across all standard electrical units and instant cross-calculation of Power (P = V × I = I²R = V²/R) in Watts (W) — giving you a complete Ohm's Law and power triangle solution in a single calculation.
This online V = IR calculator is trusted across every level of electrical and electronics engineering: A-Level, GCSE, AP Physics, JEE, and NEET Ohm's Law exam problems, DC circuit analysis — series and parallel resistor networks, LED current limiting resistor calculation, battery and power supply voltage regulation, PCB trace current capacity and voltage drop analysis, Arduino, Raspberry Pi, and electronics prototyping calculations, solar panel and battery system sizing, and electrical fault diagnosis and troubleshooting. Ohm's Law — first formulated by Georg Simon Ohm in 1827 — states that the current through a conductor is directly proportional to voltage and inversely proportional to resistance, forming the mathematical foundation of all DC circuit theory, electronics design, and electrical engineering. Trusted by students, electricians, electronics hobbyists, PCB designers, and electrical engineers worldwide.
Related Electrical & Physics Calculators
Ohm's Law Calculator — Voltage, Current, and Resistance: Solve for Any One
Ohm's Law (V = IR) is the foundational relationship of electrical circuit analysis. Every resistive circuit element, every wire, every fuse, and every heating element obeys it. A 12V battery driving current through a 6Ω resistor produces 2A of current; the same battery through a 24Ω resistor produces 0.5A. The calculator solves for voltage, current, or resistance given the other two, covering the complete range from microelectronics (millivolts and microamps) to industrial power systems (kilovolts and kiloamps) — as long as you keep units consistent.
Power dissipation in resistive elements is derived directly from Ohm's Law: P = IV = I²R = V²/R. All three forms are equivalent and give the same result, but different forms are convenient depending on what is known. A resistor carrying 3A with a resistance of 10Ω dissipates 90W — which determines whether it will overheat based on its power rating. An LED with a 2V forward voltage operating from a 5V supply with a 150Ω series resistor has 20mA flowing through it and the resistor dissipates 60mW. The calculator includes all three power forms so the thermal design check is built into the electrical calculation.
Non-ohmic components — diodes, transistors, LEDs, capacitors under AC — do not follow V = IR with a constant R. Their effective resistance changes with operating conditions. Ohm's Law still applies instantaneously at any given operating point (the dynamic resistance), but the R used must be the incremental resistance at that point, not a fixed value. The calculator is accurate for resistive components; for semiconductor analysis, it provides the linearized approximation valid near a given operating point.