Calculate volts from kW and amps
Enter load values, choose the electrical system, and calculate the estimated supply voltage.
Formula used
The calculator converts kilowatts into watts before finding voltage. Efficiency, shown as η, adjusts load power to estimated supply power.
| Circuit | Voltage formula |
|---|---|
| Direct current | V = (kW × 1000) ÷ (A × η) |
| Single-phase AC | V = (kW × 1000) ÷ (A × PF × η) |
| Three-phase AC | V = (kW × 1000) ÷ (√3 × A × PF × η) |
V means volts, kW means kilowatts, A means amps, PF means power factor, and η is efficiency as a decimal.
How to use this calculator
- Choose DC, single-phase AC, or three-phase AC.
- Enter the useful load power in kilowatts.
- Enter the expected current in amperes.
- Enter power factor for AC systems.
- Enter efficiency when conversion or equipment losses apply.
- Choose display precision and select Calculate Voltage.
- Review the result, assumptions, and export options.
Example calculations
| Circuit | kW | Amps | PF | Efficiency | Calculated volts |
|---|---|---|---|---|---|
| DC | 12 | 50 | 1.00 | 100% | 240.00 V |
| Single-phase AC | 10 | 50 | 0.80 | 95% | 263.16 V |
| Three-phase AC | 30 | 60 | 0.90 | 95% | 337.63 V |
Understanding kW, Amps, and Volts
Voltage, Power, and Current
Voltage describes electrical pressure. Power describes energy transfer over time. Current measures moving charge. These values connect through electrical formulas. This calculator starts with kilowatts and amps. It estimates the voltage your circuit needs. The chosen circuit type changes the answer. Power factor and efficiency affect it. Use measured or rated values whenever possible. Estimates guide planning, but measurements support safer installations.
Choose the Correct Circuit
Direct current uses a simple relationship. Divide watts by amps after efficiency adjustment. Single-phase alternating current also considers power factor. Power factor shows how effectively apparent power becomes useful power. Three-phase systems use an additional square-root-of-three factor. This factor reflects the relationship between line voltage and line current. Selecting the wrong circuit type produces a misleading voltage. Check the equipment label, drawings, or electrical documentation first. Residential appliances often use single-phase supply. Industrial motors and larger equipment commonly use three-phase supply.
Use Realistic Input Values
Enter load power in kilowatts. One kilowatt equals one thousand watts. Enter the measured or planned current in amperes. For alternating current, enter the expected power factor. Motors often have lower power factors at light loads. Modern electronic equipment may have correction circuits. Efficiency represents useful output divided by input power. A perfect value is one hundred percent. Real equipment loses some energy through heat, friction, and resistance. Use the manufacturer's rated efficiency when available. Keep efficiency at one hundred percent when it does not apply.
Read Results Carefully
The displayed voltage is an estimate based on your selected assumptions. It is not a substitute for design calculations or local code requirements. Compare the answer with the supply voltage available at your location. Consider voltage drop across long conductors. A correct source voltage may still deliver lower voltage at the load. Wire size, conductor material, and temperature influence voltage drop. Protective devices must also match the calculated current. Confirm ratings for switches, breakers, fuses, connectors, and cables. Never exceed equipment voltage or current limits.
For variable loads, calculate several operating points. Startup current can greatly exceed normal running current. A voltage result based only on running current cannot size every protective component. Use motor starting data, demand conditions, and applicable standards before selecting distribution equipment. Keep records of assumptions for future inspection and maintenance. Document assumptions.
Plan Safer Electrical Work
Use this tool during early sizing, troubleshooting, and equipment comparison. Record the input values with the calculated result. Download the result as CSV for project records. Use the print option to create a PDF through your browser. Recheck values after changing a motor, cable run, or supply type. Ask a qualified electrician to review critical installations. This is especially important for high voltage, three-phase, or commercial systems. Isolate power before testing. Follow lockout procedures and approved safety practices. Accurate calculations support better choices, but safe work always requires trained judgment.
Frequently asked questions
1. What does this calculator find?
It estimates supply voltage from load power in kilowatts, current in amps, circuit type, power factor, and efficiency. The result is useful for planning and checking electrical equipment assumptions.
2. Why must I choose a circuit type?
DC, single-phase AC, and three-phase AC use different voltage relationships. Three-phase calculations include the square root of three. Selecting the correct system prevents a misleading result.
3. What power factor should I enter?
Use the rated or measured power factor for AC equipment. Enter 1.000 when the load has unity power factor. DC calculations use 1.000 automatically because conventional DC power factor adjustment does not apply.
4. When should efficiency be below 100 percent?
Use a lower value when the stated kilowatts represent useful output and equipment losses matter. Motors, converters, and drives lose some energy. Use 100 percent when your kW value already represents electrical input power.
5. Does the three-phase result show phase voltage?
No. The three-phase formula returns line-to-line voltage. This is the voltage commonly used for equipment supply ratings. Phase-to-neutral voltage depends on the system connection and requires a separate relationship.
6. Can I use this for motor starting current?
You can calculate an estimated voltage using starting current. However, motor starting design needs more than this result. Review locked-rotor values, protection settings, conductor limits, and manufacturer guidance.
7. Why does a lower power factor increase voltage?
For fixed real power and current, lower power factor means less useful power per ampere. The formula therefore requires a higher voltage to produce the same kilowatt load.
8. Does this include voltage drop?
No. The result estimates voltage at the source or calculation point. Long conductors can reduce voltage at the load. Perform a separate voltage-drop calculation when cable length is significant.
9. Can I export the result?
Yes. After calculation, use Download CSV for a spreadsheet-ready record. Use Print or Save PDF to open your browser print dialog, then select a PDF destination when available.
10. Are decimal kilowatt and amp values supported?
Yes. The calculator accepts decimal values for kilowatts, amps, power factor, and efficiency. Choose up to six decimal places for displayed voltage and related values.
11. Is this suitable for final electrical design?
It is a planning and verification tool. Final electrical design should include local rules, conductor sizing, protection coordination, earthing, fault levels, voltage drop, and qualified professional review.