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Ohm's Law and Power Triangle Calculator

· Last updated：2026-06-21

Solve for two unknowns among Voltage, Current, Resistance and Power from any two given values, with visual triangles and AC power-factor support

Details

What this tool helps you do

Enter any two of V, I, R, P and the calculator derives the other two via Ohm's law (V=I·R) and power equations (P=V·I, P=I²·R, P=V²/R). AC mode applies P=V·I·cos φ and reports apparent power. Renders mnemonic Ohm's law and power triangles plus engineering SI units.

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Written by the Elysia Tools team
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Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category
Math & Numbers
Input types
number, select
Output type
html
Sample coverage
4
API ready
Yes

Overview

The Ohm's Law and Power Triangle Calculator allows you to solve for any two unknown electrical values among Voltage (V), Current (I), Resistance (R), and Power (P) when you provide any two known values. Supporting both DC and AC modes, it automatically calculates the missing parameters, applies power factor adjustments for alternating current, and renders visual mnemonic triangles alongside engineering SI units.

When to use

  • When designing or troubleshooting electrical circuits and needing to quickly determine resistance, voltage drop, or current draw.
  • When calculating power dissipation in DC components or sizing resistors to prevent overheating.
  • When analyzing AC circuits with reactive loads, such as motors or transformers, requiring power factor (cos φ) adjustments.

How it works

  1. 1Enter any two known values among Voltage (V), Current (I), Resistance (R), or Power (P), leaving the other fields blank.
  2. 2Select the circuit mode, choosing either DC (Direct Current) or AC (Alternating Current) with a specified Power Factor (cos φ).
  3. 3The calculator solves the remaining two variables using Ohm's law and power equations, displaying the results with engineering SI units and visual mnemonic triangles.

Use cases

  • Sizing a current-limiting resistor for an LED by calculating the required resistance based on target voltage drop and current.
  • Determining the current draw and apparent power of an AC electric motor using its rated wattage, voltage, and power factor.
  • Calculating the power dissipation of a heating element with a known resistance connected to a specific mains voltage.

Examples

1. Solving a Simple DC Resistor Circuit

Electronics Hobbyist

Background

A hobbyist is building a simple LED circuit and needs to determine the current and power dissipation of a 6-ohm resistor connected to a 12V DC power supply.

Problem

Manually calculating current and power to ensure the resistor does not exceed its power rating.

How to use

Enter 12 for Voltage (V), 6 for Resistance (R), select 'DC' mode, and leave the other fields blank.

V = 12, R = 6, mode = 'dc'

Outcome

The calculator determines the current is 2 A and the power dissipation is 24 W, displaying the Ohm's law and power triangles.

2. Calculating AC Motor Current Draw

Electrical Technician

Background

A technician is installing a 1500 W single-phase AC motor running on a 230 V line with a power factor (cos φ) of 0.85.

Problem

Determining the actual current draw to size the circuit breaker and wiring correctly.

How to use

Enter 230 for Voltage (V), 1500 for Power (P), select 'AC' mode, and set the Power Factor (cos φ) to 0.85.

FAQ

What is the minimum number of inputs required?

You must enter exactly two known values out of Voltage, Current, Resistance, or Power to calculate the remaining two.

How does the calculator handle AC circuits?

In AC mode, the calculator incorporates the Power Factor (cos φ) into the power equation (P = V · I · cos φ) and reports the apparent power.

What is the Power Factor (cos φ)?

It is the ratio of real power to apparent power in an AC circuit, ranging from 0 to 1, representing how effectively electrical power is converted into useful work.

Does the calculator support engineering units?

Yes, the output displays values formatted with standard engineering SI prefixes such as kΩ, mA, and mW for easier reading.

Can I calculate values for a three-phase AC system?

No, this calculator is designed for single-phase AC and DC circuits using standard Ohm's law and single-phase power equations.

Hub

Electrical Circuit Power and Cable Sizing Workflow

Calculate circuit relationships, compare resistor and capacitor formulas, convert power or energy units, and estimate voltage drop before choosing a cable size.

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V = 230, P = 1500, mode = 'ac', cosPhi = 0.85

Outcome

The calculator outputs the current draw of approximately 7.67 A and calculates the apparent power and effective impedance.