Electrical Calculator Inputs
Formula Used
| Calculation | Formula |
|---|---|
| DC watts | P = V × I |
| Single-phase AC watts | P = V × I × PF |
| Three-phase line-to-line watts | P = √3 × V × I × PF |
| Three-phase line-to-neutral watts | P = 3 × V × I × PF |
| Apparent power | S = V × I or phase-adjusted equivalent |
| Power factor | PF = P ÷ S |
| Resistance | R = V ÷ I |
| Energy | E = P × time |
| Battery runtime | Runtime = usable battery Wh ÷ load W |
How to Use This Calculator
- Select the value that you want to calculate.
- Choose DC, single-phase AC, or balanced three-phase AC.
- Enter the required electrical values and matching units.
- Add power factor, operating time, rate, and safety data.
- Press Calculate to view results, formulas, and sizing estimates.
- Copy, print, or export the completed calculation when needed.
Breaker, conductor, generator, and inverter results are preliminary estimates. Local codes and equipment instructions may require different values. A qualified electrician should verify every final installation decision.
DC, Single-Phase, and Three-Phase Calculations
DC Circuits
DC power normally equals voltage multiplied by current. Power factor does not apply to ordinary DC loads. Efficiency still affects battery and inverter planning calculations.
Single-Phase AC
Single-phase real power includes the load power factor. Apparent power remains voltage multiplied by current. Reactive power follows the AC power triangle relationship.
Three-Phase AC
Balanced line-to-line calculations use the square root of three. Line-to-neutral calculations use three times each phase value. Unbalanced systems need individual phase measurements and engineering review.
Watts, Volt-Amps, and Power Factor
Watts measure real power performing useful work. Volt-amps measure total apparent power supplied by equipment. Power factor shows how efficiently apparent power becomes real power.
A resistive heater often operates near unity power factor. Motors and transformers usually need additional reactive current. Correct sizing should use volt-amps for many AC supplies.
Example Data
| System | Voltage | Current | Power Factor | Calculated Power |
|---|---|---|---|---|
| DC | 12 V | 10 A | 1.00 | 120 W |
| Single-phase AC | 230 V | 5 A | 0.90 | 1,035 W |
| Three-phase line-to-line | 400 V | 10 A | 0.85 | 5,889 W |
| Single-phase apparent power | 120 V | 8 A | 0.80 | 960 VA and 768 W |
Frequently Asked Questions
What is the difference between watts and volt-amps?
Watts represent real power used by the load. Volt-amps represent total apparent power supplied. Power factor connects both values in AC systems.
How do I calculate watts from volts and amps?
Multiply volts by amps for a DC circuit. Include power factor for single-phase AC power. Three-phase systems also require the correct phase multiplier.
Why is power factor limited to one?
Power factor compares real power with apparent power. Real power cannot normally exceed apparent power. Values above one indicate inconsistent input data.
Does power factor apply to DC power?
Ordinary DC power uses a power factor of one. Voltage and current directly determine DC watts. Converter efficiency may still reduce delivered output power.
How is three-phase power calculated?
Line-to-line calculations use the square root of three. Line-to-neutral calculations use three phase values. The selected voltage definition must match actual measurements.
Can this calculator estimate electricity cost?
Yes, enter operating hours and electricity rate. The tool calculates selected-period, monthly, and yearly costs. Actual billing may include taxes and demand charges.
Is the breaker recommendation a final design?
No, it is only a simplified current estimate. Electrical codes include conductor and load rules. A qualified electrician must approve the final protection device.
How does battery runtime estimation work?
Battery watt-hours equal voltage multiplied by amp-hours. Usable energy includes discharge depth and efficiency. Runtime equals usable energy divided by load power.
What safety margin should I use?
Many preliminary estimates use a 20 to 25 percent margin. Motors may require extra starting capacity. Follow equipment instructions and applicable electrical codes.
Why can motor starting power be higher?
Motors can draw several times normal running current. Inverters and generators must handle that surge. Nameplate and manufacturer data provide better sizing information.
Can I use horsepower as a power input?
Yes, select horsepower beside the power field. The calculator converts mechanical horsepower into watts. Motor electrical input may be higher because of losses.
Electrical Safety Disclaimer
This calculator provides educational estimates, not installation approval. Electrical work can cause shock, fire, or equipment damage. Confirm all results using codes, manuals, and qualified professionals.