# Single-Phase and Three-Phase Power Calculation Formulas

**URL:** <https://forumautomation.com/t/single-phase-and-three-phase-power-calculation-formulas/14588>\
**Category:** Electrical\
**Tags:** basic\
**Created:** [November 11, 2026, 2:13pm UTC](https://forumautomation.com/t/single-phase-and-three-phase-power-calculation-formulas/14588 "2026-11-11T14:13:08Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [November 11, 2026, 2:13pm UTC](https://forumautomation.com/t/single-phase-and-three-phase-power-calculation-formulas/14588/1 "2026-11-11T14:13:08Z")

</div>

## Single-Phase and Three-Phase Power Calculation Formulas

**[Single-Phase and Three-Phase Power Calculation Formulas](https://forumelectrical.com/basic-electrical-engineering-formulas-and-equations/)**

## 1. Single-Phase DC Circuit

- Voltage: V = I × R

- Current: I = V / R

- Resistance: R = V / I

- Power: P = V × I

## 2. Single-Phase AC Circuit

- Active Power: P = V × I × cos φ

- Current: I = P / (V × cos φ)

- Voltage: V = P / (I × cos φ)

## 3. Three-Phase Motor

- Active Power: P = √3 × V × I × cos φ

- Current: I = P / (√3 × V × cos φ)

- Voltage: V = P / (√3 × I × cos φ)

 ![1](https://cdn.forumautomation.com/original/2X/c/c639165f177be68c88d22bb5419dc2983cb50d6f.jpeg)

## 4. Three-Phase Transformer

- Capacity: kVA = (√3 × V × I) / 1000

- Primary Current: Ip = (kVA × 1000) / (√3 × Vp)

- Secondary Current: Is = (kVA × 1000) / (√3 × Vs)

- Active Power: kW = (√3 × V × I × cos φ) / 1000

Where: V = Voltage, I = Current, R = Resistance, P = Power, cos φ = Power Factor, and √3 = 1.732.