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Current • Amps • Power

Calculate Current

Calculate the current for single-phase or three-phase systems from power, voltage and cos φ.

Calculation Values

Note: This calculation is a technically sound simplification typical of online calculators. For practical sizing, standards, installation method, temperature, grouping, protective devices, cable type and manufacturer specifications must also be checked.

Formula Used

Single-phase: I = P / (U × cos φ)

Three-phase: I = P / (√3 × U × cos φ)

FAQ

Frequently Asked Questions about Calculate Current

Briefly explained: formula, use case and key limits of the calculation.

What does the current calculator determine? +

The calculator determines the current in amps from power, voltage, system type and power factor.

Why are there different formulas? +

Single-phase and three-phase systems have different electrical relationships. Three-phase additionally accounts for √3.

What is the difference between watts and amps? +

Watts describe power, amps describe current. The relationship depends on voltage, system type and power factor.

Is the result sufficient for sizing protective devices? +

No. Sizing protective devices and cables requires checking further technical conditions.

Practical guidance

Calculate amperes for the correct electrical system

The general current calculator shows why equal active power produces different currents in single- and three-phase systems.

Input values explained

Current type
The current type determines whether the calculation uses factor 2 for outgoing and return conductors or √3 for balanced three-phase power.
Power in watts
Use the electrical active power drawn by the load. A nameplate, data sheet or power meter is more reliable than an estimate.
Voltage
Match the voltage to the selected electrical system. Single-phase calculations use line-to-neutral voltage, while three-phase calculations use voltage between two line conductors.
Power factor cos φ
cos φ is the ratio of active to apparent power. It is close to 1 for resistive heating loads; use the data-sheet value for motors and transformers.

Example: 3,500 W at 230 V

A single-phase load takes 3,500 W at 230 V with a power factor of 0.90.

I = 3,500 W ÷ (230 V × 0.90) ≈ 16.91 A

The calculated operating current is 16.91 A. With a resistive load at cos φ 1 it would be about 15.22 A.

Current is not a fuse rating

This is steady operating current. A cable or protective device must not be selected merely by rounding it up.

Calculation limits

  • Efficiency, inrush, harmonics and short peaks are excluded.
  • The balanced formula is unsuitable for an unbalanced three-phase load.