kW to Volts Calculator
Solve for voltage when you know real power and current. Useful for verifying nameplate ratings and sizing conductors.
Common conversions
| Input | Result |
|---|---|
| 1.2 kW, 10 A (PF 1) | 120 V |
| 3.6 kW, 30 A (PF 1) | 120 V |
| 4.8 kW, 20 A (PF 1) | 240 V |
| 7.2 kW, 30 A (PF 1) | 240 V |
| 6.48 kW, 30 A (PF 0.9) | 240 V |
| 10 kW, 25 A (PF 0.85, 1φ) | ≈470.59 V |
| 22.45 kW 3φ, 30 A (PF 0.9) | ≈480 V |
| 0.12 kW DC, 10 A | 12 V |
The math behind it
- V = (9.6 × 1000) / (40 × 1)
- V = 9,600 / 40
Everything you need to know
Voltage is usually fixed by the electrical supply, so solving for it is less common than solving for amps or kW. This calculator reverses the usual math: given real power and current, it tells you what voltage would produce that reading, which is useful for verifying a nameplate or catching a wiring mismatch rather than for designing a new circuit.
Why reverse-solve for voltage
Electricians and technicians rarely choose a supply voltage; it's set by the utility transformer or the equipment's design. What this calculator is good for is sanity-checking: if a motor's nameplate lists 4.8 kW, 20 A, and PF 1.0, plugging those numbers in should return a standard voltage like 240 V. If it returns something unexpected, like 300 V, one of the three input numbers is likely wrong or misread.
Standard voltages to check against
In US practice, calculated voltage should land close to a standard value: 120 V for single-phase receptacles, 208 V for line-to-line voltage on a 120/208 V three-phase system, 240 V for split-phase residential service, or 480 V for larger commercial and industrial three-phase distribution. A small gap, a few percent below the standard, usually reflects normal voltage sag under load rather than an error.
Single-phase vs three-phase
The single-phase formula, V = kW × 1000 / (A × PF), works for standard residential and light-commercial circuits. Three-phase line-to-line voltage needs the √3 divisor: V = kW × 1000 / (√3 × A × PF). A 22.45 kW three-phase load at 30 A and PF 0.9 comes back to about 480 V; using the single-phase formula on the same numbers would wrongly suggest about 831 V.
Common applications
Manufacturers list kW, amps, and PF separately. Back-calculating voltage confirms the nameplate is internally consistent before connecting equipment to a specific supply.
If the calculated voltage comes out well below the nominal 120, 240, or 480 V supply, it can indicate undersized conductors, a loose connection, or an overloaded transformer.
A generator rated for 6.48 kW at 27 A and PF 0.9 should read close to 240 V. A large deviation points to a miscalibrated meter or a generator problem.
Reverse-solving for voltage from power and current builds intuition for how V, A, kW, and PF relate, which helps when reading multimeter and clamp meter results in the field.
Common mistakes
Voltage is fixed by the electrical supply. This calculator checks or verifies a value; it can't be used to specify a new service voltage for an installation.
Leaving PF at 1 for a motor or compressor understates the true voltage needed to explain the measured kW and amps, sometimes by 10-20%.
Single-phase and three-phase voltage formulas differ by a factor of √3. Applying the single-phase formula to a three-phase reading gives a voltage about 73% too high.
A calculated voltage of 228 V instead of 240 V isn't necessarily an error; real circuits commonly sag 3-5% under load.
Frequently asked questions
Why would I need to calculate voltage instead of just reading it off the panel?+
Because you're checking whether a measured kW and amp reading matches the expected supply voltage. A mismatch usually flags a wiring error, a mislabeled panel, or voltage sag under load.
Can I choose any voltage by changing kW or amps?+
No. Supply voltage is fixed by the utility or transformer. This calculator verifies or reverse-engineers voltage, it doesn't let you select one for an installation.
How many volts is 4.8 kW at 20 A?+
240 V, using V = 4,800 / 20 with PF 1.0.
Does power factor change the calculated voltage?+
Yes. A lower power factor raises the calculated voltage for the same kW and amps, because dividing by a smaller PF increases the result.
What if my calculated voltage doesn't match a standard value?+
Small differences from 120, 240, or 480 V are normal due to voltage sag, rounding on the nameplate, or an inaccurate PF assumption. Differences over 10% suggest measurement error or a wiring problem.
Is this the same as Ohm's law?+
It's related but not identical. Ohm's law relates voltage, current, and resistance (V = I × R); this calculator relates voltage, real power, current, and power factor for AC systems.
How do I find voltage for a three-phase circuit?+
Use V = kW × 1000 / (√3 × A × PF) for line-to-line voltage. A 22.45 kW three-phase load at 30 A and PF 0.9 works out to about 480 V.
Do I need this calculator for DC circuits?+
Yes, but PF simply equals 1, which simplifies the formula to V = kW × 1000 / A.
Why is my calculated voltage lower than expected?+
A lower-than-expected result usually means the amps or kW value entered is too high, or the power factor entered is too low. Double-check nameplate figures before troubleshooting wiring.