True Power Calculator

Inputs

System Type DC Single-phase AC Three-phase AC

For three-phase, use line-to-line voltage and line current.

Voltage

V mV kV

RMS voltage for AC systems.

Current

A mA kA

Use line current for three-phase.

Power Factor (0–1)

PF = P / S. For DC it becomes 1.

Efficiency (%)

Use 100% to ignore losses.

Run Time

hours minutes

Used to compute energy and cost.

Electricity Rate (optional)

per kWh

Leave blank to skip cost.

Notes (optional)

Notes appear in the PDF summary.

Submit Load Example Print

Example Data Table

Formula Used

• DC: P = V × I
• Single-phase AC: P = V × I × PF
• Three-phase AC: P = √3 × V_L × I_L × PF
• Apparent power: S = V × I (single) or S = √3 × V_L × I_L (three)
• Reactive power: Q = √(S² − P²)
• Energy: E(kWh) = P(W) ÷ 1000 × time(hours)
• Delivered power: P_out = P × (efficiency ÷ 100)

How to Use This Calculator

1. Select the system type: DC, single-phase AC, or three-phase AC.
2. Enter voltage and current with the correct units.
3. For AC loads, enter the power factor from the nameplate or meter.
4. Set efficiency to estimate delivered power after losses.
5. Optionally add run time and a rate to estimate energy and cost.
6. Press Submit. Results appear above the form under the header.
7. Download CSV for saved runs or PDF for a report-style summary.

Why True Power Matters

True power is the rate electrical energy becomes work or heat. Utilities bill in kilowatt-hours, so the real-power value drives operating cost directly. When a device shows high current but low power factor, conductors still carry the current while delivering less usable power. That mismatch increases losses and can push equipment toward thermal limits.

Inputs That Drive Accuracy

Use measured RMS voltage and current in the same window. Clamp meters and power analyzers can disagree under distorted waveforms, so record harmonics when possible. For motors, take power factor from a meter rather than a nameplate at light load. If you estimate efficiency, keep it conservative because delivered power scales directly with the percentage.

Single-Phase vs Three-Phase Behavior

Single-phase apparent power is V×I, while three-phase uses √3×V_L×I_L. Enter line-to-line voltage and line current for balanced systems. A small change in power factor affects three-phase totals quickly, because the √3 multiplier magnifies the base apparent power. This calculator keeps that relationship explicit for troubleshooting.

Interpreting Apparent and Reactive Power

Apparent power shows how much current the supply must deliver, regardless of how effectively the load converts it. Reactive power represents the exchange between magnetic or electric fields and the source. Using Q=√(S²−P²), you can estimate how much reactive support is present. Large Q relative to P often indicates opportunities for correction capacitors or drive tuning.

Energy, Cost, and Efficiency Decisions

Energy equals real power multiplied by time, so even modest reductions in P can yield savings over long run hours. Compare input energy to delivered energy to quantify losses. If you add a rate, the tool computes an estimated cost from input kWh, which matches typical billing. Use the history table to benchmark before-and-after maintenance, filters, or control changes.

Field Measurement Tips

Verify instrument range, then capture steady-state values after inrush settles. For variable-frequency drives, measure on the input side to reflect supply loading. Check connections, phase rotation, and current balance on three-phase systems. If power factor changes across operating points, log several runs and export CSV for analysis. Consistent sampling improves repeatability and supports engineering decisions.

FAQs

1) What is true power?

True power is the real, usable power consumed by a load. It equals voltage times current times power factor for AC, and voltage times current for DC.

2) Why can current be high while true power is low?

When power factor is low, current still flows to support reactive fields. Apparent power rises, but the portion converted to work or heat, true power, remains smaller.

3) Which voltage should I enter for three-phase?

Enter line-to-line voltage and line current for typical three-phase measurements. The calculator applies the √3 relationship used for balanced three-phase power calculations.

4) How is reactive power calculated here?

Reactive power is derived from the power triangle using Q = √(S² − P²). This uses apparent power S and true power P to estimate field-related power exchange.

5) What does the efficiency setting change?

Efficiency scales delivered power and delivered energy. Input true power still reflects what the supply provides, while delivered values estimate what reaches the mechanical or thermal output.

6) Does the cost estimate match my bill?

It estimates cost from input kWh multiplied by your rate. Bills may include demand charges, taxes, and tiered pricing, so treat the cost output as a practical approximation.