Example Data Table
| System |
Voltage |
Current |
Power factor |
Formula |
Power |
| DC circuit |
12 V |
8 A |
1 |
P = V × I |
96 W |
| Single phase AC |
230 V |
10 A |
0.90 |
P = V × I × PF |
2,070 W |
| Three phase AC |
400 V |
20 A |
0.85 |
P = √3 × V × I × PF |
11,777.95 W |
Formula Used
DC power: P = V × I
Single phase AC power: P = V × I × PF
Three phase line-line power: P = √3 × VLL × I × PF
Three phase line-neutral power: P = 3 × VLN × I × PF
Apparent power: S = V × I for DC and single phase. For three phase, S = √3 × VLL × I.
Energy: kWh = kW × operating hours × operating days
Cost: Cost = kWh × energy rate
How to Use This Calculator
Select the system type first. Enter voltage and current values. Choose the matching units. Add power factor for AC loads. Use 1 for ideal resistive loads. Add efficiency if output power is lower than input power. Enter operating time and energy rate. Press Calculate to see the result above the form. Use CSV or PDF for records.
Power From Current and Voltage Guide
Why This Calculation Matters
Electrical power shows how fast a circuit uses energy. It helps size wires, breakers, inverters, generators, and battery systems. A small error can affect safety. It can also change running cost. This calculator keeps the process clear. It accepts common field inputs. It also handles DC, single phase AC, and three phase AC loads.
Current, Voltage, and Load Behavior
Voltage is electrical pressure. Current is the flow through the load. Their product gives basic power for DC circuits. AC systems need one more value. That value is power factor. Motors, transformers, compressors, and ballasts may not use all apparent power as real power. Power factor corrects that difference. A lower value means more current is needed for the same useful output.
Single Phase and Three Phase Use
Single phase service is common in homes and small shops. Three phase service is common in plants, pumps, and commercial panels. Three phase power can be calculated with line-line voltage or line-neutral voltage. The selected method must match the measured voltage. Using the wrong type can create a large error. Always check the meter points before entering values.
Efficiency, Energy, and Cost
Efficiency adjusts the power that becomes useful output. No real device is perfect. Heat, friction, magnetic losses, and electronics reduce usable power. The calculator also estimates energy in kilowatt-hours. This is helpful for monthly cost checks. Enter hours, days, and rate. The result shows expected energy use and cost for the chosen load period.
Safety Margin and Practical Checks
The safety margin field helps with planning. It raises the calculated power by a chosen percentage. This is useful when loads start hard or may expand later. It does not replace electrical codes. Breaker size, conductor rating, insulation, temperature, duty cycle, and local rules still matter. For critical circuits, confirm values with a qualified electrician.
FAQs
1. What is the basic power formula?
The basic formula is P = V × I. It works directly for DC circuits and simple resistive loads. AC circuits often need power factor for a more realistic real power value.
2. Why does AC power need power factor?
Power factor accounts for phase shift between voltage and current. Motors and inductive loads draw apparent power that is not fully converted into real work. The calculator uses power factor to estimate real watts.
3. What power factor should I enter?
Use the value from the equipment label or datasheet. If unknown, 1 works for resistive heaters and lamps. Motors often range from 0.75 to 0.95, depending on design and load.
4. How is three phase power calculated?
For line-line voltage, the formula is P = √3 × V × I × PF. For line-neutral voltage, the formula is P = 3 × V × I × PF.
5. What is apparent power?
Apparent power is measured in VA. It shows the combined effect of voltage and current before power factor correction. It helps size transformers, UPS units, and generators.
6. What does the efficiency field do?
Efficiency reduces calculated input power to useful output power. Enter 100 for no adjustment. Use a lower value when estimating motor shaft output or delivered device power.
7. Can this calculator estimate electricity cost?
Yes. Enter operating hours, days, and energy rate. The calculator converts watts to kilowatts, then estimates kilowatt-hours and cost for the selected period.
8. Is this enough for breaker sizing?
No. It is a planning aid only. Breaker sizing also depends on code rules, conductor rating, ambient temperature, load type, duty cycle, and starting current.