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Ohm's Law Calculator

Everyday

Calculate voltage, current, resistance, or power using Ohm's Law (V=IR, P=IV). Enter any two known electrical values to find all four quantities instantly.

Reviewed by the thecalcu.com team · Last updated June 24, 2026

Solve For
Known Values
Amps
Ohms
Formulae
V = I × R
I = V / R
R = V / I
P = V × I
Voltage
—
Volts
All Values
VSOLVED
—
Volts
I
—
Amps
R
—
Ohms (Ω)
P
—
Watts
Equation used: V = I × R

What is a Ohm's Law?

Ohm's Law is the most fundamental relationship in electrical engineering: the voltage across a conductor equals the product of the current flowing through it and its resistance (V = I × R). First formulated by German physicist Georg Simon Ohm in 1827, this simple equation underpins the analysis of every electrical circuit, from the wiring in your home to the transistors in your smartphone.

The Ohm's Law Calculator extends the basic formula to all four interrelated electrical quantities: Voltage (V), Current (I), Resistance (R), and Power (P). By entering any two known values, you can instantly calculate the remaining two. This is invaluable for students learning circuit theory, electricians sizing wires and fuses, hobbyists building electronics, and engineers troubleshooting electrical faults.

In the Indian context, Ohm's Law is directly relevant to understanding your household electrical system, which operates at 230 V AC / 50 Hz. Questions like "how much current does my 1,500 W geyser draw?" (answer: 1,500 ÷ 230 ≈ 6.5 A) or "what is the resistance of my 60 W bulb at operating temperature?" (answer: 230² ÷ 60 ≈ 882 Ω) are straightforward Ohm's Law calculations. The Voltage Drop Calculator builds on Ohm's Law to help you size electrical cables for safe, compliant installations.

Why Use the Ohm's Law Calculator?

Solve for any of four variables. The calculator presents four input modes, Voltage, Current, Resistance, and Power, so you start from whichever two quantities you know. You do not need to remember which rearrangement of the formula to use.

See all quantities simultaneously. Even when you solve for just one unknown, the calculator displays all four values side by side, giving you a complete picture of the circuit's electrical behaviour.

Learn the formula used. Each calculation shows which specific equation was applied, making it an effective learning tool for engineering students preparing for examinations.

Handle large and small values. The calculator formats outputs intelligently, milliamps for small currents, kilohms and megaohms for large resistances, avoiding scientific notation that can be hard to interpret at a glance.

Who Should Use This Calculator?

Engineering and diploma students studying Basic Electrical Engineering or Applied Physics routinely solve Ohm's Law problems. This calculator checks manual work and allows rapid what-if exploration.

Electricians and panel builders can quickly verify that a proposed circuit, a specific cable gauge, rated load, and supply voltage, is within safe operating parameters without carrying a dedicated tester.

Electronics hobbyists building Arduino or Raspberry Pi circuits need to size resistors for LEDs, calculate collector currents for transistors, or check power dissipation in components, all Ohm's Law applications.

Homeowners who want to understand why a fuse blew, how much current a large appliance draws, or whether a circuit is overloaded can use the calculator to get quick answers without specialist knowledge.

Energy auditors checking the power consumption of specific appliances from their nameplate ratings can use P = V × I to verify or cross-check manufacturer specifications.

What Insights Does the Ohm's Law Calculator Give You?

Voltage (V), the electrical potential driving the circuit. In household contexts, this is typically 230 V in India or 120 V / 240 V in the US. For battery-powered circuits, it is the battery voltage (1.5 V, 9 V, 12 V, etc.).

Current (A), how much charge flows per second. High current values mean more heat generation in wires, so this figure is critical for fuse and cable sizing. A 10 A current needs wiring rated for at least 10 A with an appropriate safety margin.

Resistance (Ω), the opposition the circuit presents to current flow. For heating elements (geysers, room heaters), resistance is low; for incandescent bulbs, the operating resistance is much higher than the cold resistance due to the positive temperature coefficient of tungsten.

Power (W), the rate of energy consumption or dissipation. This directly translates to electricity units on your bill (1 kWh = 1,000 W × 1 hour). High power dissipation in a component means it will run hot and may require a heat sink.

How to use this Ohm's Law calculator

  1. Select what to Solve For, click one of the four coloured buttons: Voltage (V), Current (I), Resistance (R), or Power (W). This determines which unknown the calculator will find.
  2. Enter two known values, the calculator shows input fields for the remaining three quantities; provide any two of them. For example, if solving for Resistance, enter Voltage and Current (or Power and Voltage).
  3. Read all four results, the solved value is highlighted with a "SOLVED" badge. All four quantities are shown in a 2×2 grid so you can immediately see the complete electrical picture.
  4. Check the formula, a footer line shows which formula was applied (e.g., R = V ÷ I), useful for study or verification.

Formula & Methodology

The four interrelated formulas derived from Ohm's Law and the power equation P = V × I:

Solving for Voltage: V = I × R; also V = P ÷ I; also V = √(P × R)

Solving for Current: I = V ÷ R; also I = P ÷ V; also I = √(P ÷ R)

Solving for Resistance: R = V ÷ I; also R = V² ÷ P; also R = P ÷ I²

Solving for Power: P = V × I; also P = I² × R; also P = V² ÷ R

Worked example: An electrician in Chennai needs to check whether a 1,500 W room heater connected to a 230 V supply is drawing safe current.

- Solving for Current: I = P ÷ V = 1,500 ÷ 230 = 6.52 A
- Resistance of the heating element: R = V ÷ I = 230 ÷ 6.52 = 35.28 Ω
- Verification: P = I² × R = 6.52² × 35.28 = 42.51 × 35.28 ≈ 1,500 W ✓

The heater draws 6.52 A. A 15 A MCB protecting the circuit is adequate. A 10 A MCB would be marginal, acceptable but providing less headroom. The electrician knows to use wiring rated for at least 10 A (2.5 mm² copper conductor) for this circuit.

Frequently Asked Questions

Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance: V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. It is the foundational relationship of basic circuit analysis, formulated by German physicist Georg Simon Ohm in 1827.
The four interrelated formulas are: V = I × R (voltage), I = V ÷ R (current), R = V ÷ I (resistance), and P = V × I (power, also P = I²R = V²/R). Knowing any two of the four quantities, voltage, current, resistance, and power, allows you to calculate the other two.
Power (W) = Voltage (V) × Current (A). This is derived from the basic power formula P = W/t combined with Ohm's Law. Equivalently, P = I² × R or P = V² ÷ R. The Ohm's Law Calculator computes all four values simultaneously once you provide any two known quantities.
Voltage is measured in Volts (V), current in Amperes or Amps (A), resistance in Ohms (Ω), and power in Watts (W). For very large or small values, prefixes are used: milliamps (mA = 0.001 A), kilohms (kΩ = 1,000 Ω), megaohms (MΩ = 1,000,000 Ω), and kilowatts (kW = 1,000 W).
Select which quantity you want to solve for (V, I, R, or P) using the four mode buttons. Then enter any two of the remaining known values. The calculator instantly computes all four quantities and highlights the solved value. It also displays the specific formula used, so you can learn the relationship.
Ohm's Law in its basic V = IR form applies to DC (direct current) circuits and to purely resistive AC loads. In AC circuits with capacitors or inductors, the concept of impedance (Z) replaces resistance (R), and the formula becomes V = I × Z. For standard resistive appliances on Indian 230V AC supply, the basic Ohm's Law formulas give correct results.
Indian residential electricity uses 230 V AC at 50 Hz, as specified by the Bureau of Indian Standards. This is the standard across South Asia. North America uses 120 V / 60 Hz and 240 V for heavy appliances. Always verify the rated voltage on any appliance before connecting it, using a 120V device on a 230V Indian supply without a transformer will damage or destroy the device.
Voltage is electrical pressure, the force pushing electrons through a circuit, measured in Volts. Current is the rate of electron flow, measured in Amperes. Resistance is the opposition to that flow, measured in Ohms. A helpful analogy is water in a pipe: voltage is the water pressure, current is the flow rate, and resistance is the pipe's narrowness.
Use the formula R = V ÷ I. If an appliance rated at 230 V draws 2 A of current, its resistance is 115 Ω. Alternatively, R = V² ÷ P, a 230 V, 1,000 W appliance has a resistance of 230² ÷ 1,000 = 52.9 Ω. You can measure actual resistance directly with a multimeter (with the appliance unplugged).
Electrical power input (V × I) is what the device consumes from the supply. Some of that is converted to useful output (light, heat, mechanical work) and some is lost as heat in the wiring, motor windings, or other components. Efficiency = Useful Output ÷ Total Input. Most real-world devices are 60–95% efficient. Ohm's Law describes the electrical input side, not the mechanical output efficiency.
Standard Indian household wiring uses copper conductors of 1.5 mm² (for lighting circuits, rated up to 15 A) and 2.5 mm² (for power sockets, rated up to 20 A). Using more current than the wire's rated capacity causes overheating and fire risk. Always use properly rated wires, fuses, or MCBs (miniature circuit breakers) to protect circuits. See the [Voltage Drop Calculator](/voltage-drop-calculator/) for wire sizing checks.
Also known as
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