Alternating Current Calculator
Use this tool to solve single-phase AC power triangle values and component reactance. Great for quick electrical checks, homework, and practical design work.
1) AC Power Triangle (Single-Phase)
Enter any 3 of these 4 values: Voltage, Current, Power Factor, Real Power. The calculator finds the missing value and then computes apparent/reactive power.
2) Reactance Calculator
Find inductive reactance (XL) and/or capacitive reactance (XC) at a chosen frequency.
Note: This calculator assumes ideal components. Real-world coils and capacitors have resistance/losses.
What is an alternating current calculator?
An alternating current (AC) calculator helps you quickly compute electrical values that are common in household, industrial, and lab power systems. Unlike direct current (DC), AC changes direction periodically. Because of this, AC calculations often involve concepts such as RMS voltage, power factor, apparent power, and reactive power.
This page includes two useful tools:
- AC power triangle calculator for single-phase systems
- Reactance calculator for inductors and capacitors at a specific frequency
Core AC formulas used
Single-phase power relationships
- Apparent Power:
S = V × I(VA) - Real Power:
P = V × I × PF(W) - Reactive Power:
Q = √(S² − P²)(VAR) - Power Factor:
PF = P / S - Phase Angle:
θ = cos⁻¹(PF)
Reactance relationships
- Inductive reactance:
XL = 2πfL - Capacitive reactance:
XC = 1 / (2πfC) - LC resonance frequency (ideal):
fr = 1 / (2π√LC)
How to use this calculator
For AC power triangle
Enter any three values from voltage, current, power factor, and real power. Leave one blank. Click Calculate AC Power. The missing value will be computed and shown with apparent power, reactive power, and phase angle.
For reactance
Enter frequency first. Then enter inductance, capacitance, or both. Click Calculate Reactance to see XL, XC, and optional resonance frequency if both components are provided.
Worked examples
Example 1: Find real power
Given V = 230 V, I = 10 A, PF = 0.85:
P = 230 × 10 × 0.85 = 1955 WS = 230 × 10 = 2300 VA- Reactive power is
Q = √(2300² − 1955²)
Example 2: Find current for a load
Suppose a machine needs 3000 W at 240 V with PF = 0.9:
I = P / (V × PF) = 3000 / (240 × 0.9) ≈ 13.89 A
Example 3: Inductor reactance
At 60 Hz with L = 50 mH (0.05 H):
XL = 2π × 60 × 0.05 ≈ 18.85 Ω
Why power factor matters
Low power factor means your system draws more current than necessary for the same useful power output. That can increase cable losses, voltage drop, and utility penalties in commercial environments. Power factor correction (often using capacitors) can improve efficiency and reduce operating cost.
Practical notes and safety
- Use RMS values for AC voltage and current unless otherwise stated.
- Verify instrument accuracy before trusting a calculation.
- For three-phase systems, formulas differ from single-phase values shown here.
- Always follow electrical safety standards and lockout procedures when testing live equipment.
Quick FAQ
Is this for DC circuits?
No. This calculator is designed for alternating current conditions and AC component behavior.
Can I use this for three-phase motors?
Only as a rough reference. Proper three-phase calculations require line-to-line/line-to-neutral context and dedicated formulas.
Why do I get an error saying power is too high?
Real power cannot exceed apparent power in a valid AC power triangle. Check units and make sure PF is between 0 and 1.