Ohm's Law Calculator

Name: Ohm's Law Calculator
Author: Jitendra Kumar

Solve voltage, current, resistance, and power from any two known values, then estimate runtime energy and electricity cost.

Last Updated: May 2026

Known values

R = V / I, P = V x I

Runtime

Optional energy and cost estimate.

Electricity rate

$/ kWh

Voltage

Current

Voltage

12V

Current

Resistance

6ohms

Power

24W

Formula used

R = V / I, P = V x I

Current

2,000 mA

Energy

0.120 kWh

Runtime cost

$0.02

Quantity	Result	Formula context
Voltage	12 V	V = I x R, or from power/current depending on mode.
Current	2 A	I = V / R, or from power/voltage depending on mode.
Resistance	6 ohms	R = V / I, or from voltage/current/power relationships.
Power	24 W	P = V x I = I^2 x R = V^2 / R.

Runtime view	Result	Calculation note
Runtime energy	0.120 kWh	Power in watts x hours / 1,000.
Runtime cost	$0.02	Energy kWh multiplied by cost per kWh.
Current in mA	2,000 mA	Useful for electronics and low-current circuits.
Resistance in kohms	0.006 kohms	Useful for electronics resistor values.

Core law

Ohm's Law relates voltage, current, and resistance: voltage equals current times resistance.

Power note

Power can be calculated as V x I, I squared x R, or V squared divided by R for simple resistive circuits.

Safety note

Real circuits can include tolerance, temperature rise, AC phase angle, inductance, capacitance, and protective-device requirements.

Electrical Safety Notice

This calculator is educational and is not electrical design approval. Real circuits can include tolerance, heat rise, inrush current, AC impedance, power factor, insulation, grounding, conductor ampacity, protective-device coordination, and code requirements. Confirm practical designs with qualified electrical professionals and manufacturer data.

Reviewed For Methodology, Labels, And Sources

Every CalculatorWallah calculator is published with visible update labeling, linked source references, and founder-led review of formula clarity on trust-sensitive topics. Use results as planning support, then verify institution-, policy-, or jurisdiction-specific rules where they apply.

Reviewed By

Jitendra Kumar, Founder & Editorial Standards Lead, oversees methodology standards and trust-sensitive publishing decisions.

Review editor profile

Topic Ownership

Sales tax and tax-sensitive estimate tools, Education and GPA planning calculators, Health, protein, and screening-formula pages, Platform-wide publishing standards and methodology

See ownership standards

Methodology & Updates

Page updated May 2026. Trust-critical pages are reviewed when official rates or rules change. Evergreen calculator guides are checked on a recurring quarterly or annual cycle depending on topic volatility.

Sources & methodology About the review process

How to Use the Ohm's Law Calculator

Choose the two known quantities, enter their values, and the calculator derives the remaining voltage, current, resistance, and power values. Runtime and cost fields are optional but useful when the circuit will operate for a known number of hours.

Use volts for voltage, amperes for current, ohms for resistance, and watts for power. The results also show current in milliamps, resistance in kohms, energy in kWh, and runtime cost.

Step 1: Choose known values
Select the pair you know, such as voltage and current or voltage and resistance.
Step 2: Enter circuit values
Type positive values for the selected quantities using volts, amperes, ohms, or watts.
Step 3: Add runtime context
Enter hours and cost per kWh if you want energy and cost estimates.
Step 4: Review results
Check voltage, current, resistance, power, formula context, energy, and cost.

How This Ohm's Law Calculator Works

Ohm's Law relates voltage, current, and resistance with the equation V = I x R. The calculator rearranges that relationship based on the two values you enter.

Power is calculated with P = V x I. For simple resistive circuits, equivalent formulas are P = I squared x R and P = V squared divided by R. Runtime energy uses kWh = watts x hours / 1,000.

These formulas are ideal for basic DC and resistive examples. For AC loads with motors, coils, capacitors, or non-unity power factor, treat this as simplified context rather than a full circuit model.

Ohm's Law and Power Guide

Core Formulas

Quantity	Formula	Use
Voltage	V = I x R	Use current in amperes and resistance in ohms.
Current	I = V / R	Use voltage in volts and resistance in ohms.
Resistance	R = V / I	Use voltage in volts and current in amperes.
Power	P = V x I	Equivalent forms include P = I^2 x R and P = V^2 / R.
Energy	kWh = W x hours / 1,000	Useful for runtime and electricity-cost estimates.

Practical Cautions

Topic	Why it matters	Planning note
Resistor tolerance	Actual resistance can differ from nominal value.	Check component tolerance and temperature coefficient.
Power rating	Parts can overheat if wattage rating is too low.	Select a rating with adequate margin for heat and enclosure conditions.
AC circuits	Reactive loads have phase angle and impedance.	Ohm's Law alone is simplified for non-resistive AC loads.
Wiring and protection	Current affects conductor sizing and overcurrent protection.	Use electrical codes and qualified review for real installations.

Ohm's Law is the starting point for circuit intuition, but real design also depends on component ratings, conductor size, thermal behavior, enclosure temperature, and safety margins.

After finding current and power, use the Electrical Cable/Wire Size and Voltage Drop Calculator for conductor planning, or the Electricity Cost Calculator for longer runtime cost checks.

Keep the research moving with Electrical Cable/Wire Size and Voltage Drop Calculator, Conduit and Wire Fill Calculator, Electricity Cost Calculator, and Power Converter.

Frequently Asked Questions

Ohm's Law states that voltage equals current multiplied by resistance: V = I x R. Rearranged forms solve current as I = V / R and resistance as R = V / I.

Power can be calculated as P = V x I. Equivalent resistive-circuit formulas are P = I^2 x R and P = V^2 / R.

Yes. This calculator supports voltage-current, voltage-resistance, current-resistance, voltage-power, current-power, and resistance-power input pairs.

It works best for simple resistive loads. AC circuits with motors, transformers, capacitors, inductors, or power factor need impedance and phase-angle analysis.

No. It is an educational calculator. Real electrical work requires code compliance, component ratings, heat checks, protective devices, and qualified review.