⚡
ElectroBoard/Tools/Converter W ↔ A ↔ V
Open constructor →
⚡ CONVERTER

Power calculator: Watts ↔ Amps ↔ Volts

Calculation of current, active and apparent power (W and VA) for single-phase, three-phase and DC networks. Power factor cos φ, circuit breaker, cable cross-section.

QUICK SELECTION:

⚙️ Parameters

1 kW = 1000 W
0.50 (motor)0.95 (appliance)1.00 (heater)
Heater/element: 1.0 · Motor: 0.75–0.85 · Appliance: 0.90–0.95
📐 Formula:
I = P / (U × cos φ) = P / (220 × 0.95)

📊 Result (1ph 220V)

Current9.57 A
Active power2.000 kW
Apparent power2.105 kVA
Voltage220 V

🔌 Recommendations

MCB
C13
In ≥ 10.5 A
CABLE
VVGng 1.5 mm²
when laid in a pipe

📋 Reference: kW → A (220V, cos φ 0.95)

1 kW4.8 A
1.5 kW7.2 A
2 kW9.6 A
2.5 kW12 A
3 kW14.4 A
3.5 kW16.8 A
4 kW19.2 A
5 kW24 A
7.5 kW35.9 A
10 kW47.8 A

Calculation formula: Watts → Amps

Single-phase network (220V)
I = P / (U × cos φ)
Kettle 2 kW: I = 2000 / (220 × 1.0) = 9.1 A
Three-phase network (380V)
I = P / (√3 × U × cos φ)
Motor 10 kW: I = 10000 / (1.732 × 380 × 0.85) = 17.9 A
DC network
I = P / U
Inverter 1.2 kW, 48V: I = 1200 / 48 = 25 A

How to convert watts to amps?

For single-phase network 220V: I (A) = P (W) / (220 × cos φ). At cos φ = 1.0 (heaters, heating elements): 1 kW = 4.55 A. At cos φ = 0.95 (household appliances): 1 kW = 4.79 A. At cos φ = 0.8 (motors): 1 kW = 5.68 A.

For three-phase network 380V: I = P / (√3 × 380 × cos φ) = P / (658 × cos φ). At cos φ = 0.85: 10 kW = 17.9 A per phase. The current of a three-phase load is almost three times less than that of a single-phase load at the same power.

After calculating the current, select a circuit breaker from the standard range (6, 10, 16, 20, 25, 32, 40 A) with a rating of at least 110% of the calculated current. Choose the cable cross-section according to the table of permissible currents from IEC 60364.

For three-phase circuits, it is important to distribute the load evenly across phases. If you have calculated the current for a three-phase device (e.g., a 10 kW motor = 17.9 A per phase), check the phase balance in the phase balance calculator — the imbalance should not exceed 15–20% according to IEC 60364.

To select a cable based on the calculated current, use the cable cross-section calculator — it takes into account line length, material, installation method, and permissible voltage drop.

Watts, volt-amperes, and kilowatts — what is the difference?

Watt (W) is active power that performs useful work: heating, rotation, lighting. Volt-ampere (VA) is apparent power consumed by the device from the grid, including reactive component. For heaters and lamps, W = VA (cos φ = 1). For motors and compressors, VA > W.

DevicePower, Wcos φApparent power, VACurrent, A (220V)
Kettle 2 kW2 0001.002 000 VA (2 kVA)9.1
Boiler 2 kW2 0001.002 000 VA (2 kVA)9.1
Air conditioner 2.5 kW2 5000.852 941 VA (2.9 kVA)13.4
Washing machine 2 kW2 0000.852 353 VA (2.4 kVA)10.7
Motor 5.5 kW5 5000.826 707 VA (6.7 kVA)30.5
Welding machine 5 kW5 0000.707 143 VA (7.1 kVA)32.5

UPS (uninterruptible power supply) and generators specify power in VA. To determine how many watts they can handle, multiply VA by the load's cos φ (typically 0.6–0.8 for office equipment).

Frequently asked questions

How many amps in 1 kilowatt at 220V?
At 220V and cos φ = 1.0: 1 kW = 4.55 A. At cos φ = 0.95 (typical for household appliances): 1 kW = 4.79 A. Formula: I = P / (U × cos φ). For three-phase network 380V: 1 kW = 1.52 A (cos φ = 1.0).
How to calculate current for a three-phase network?
For three-phase network: I = P / (√3 × U × cos φ), where U is line voltage (380V). Example: electric motor 10 kW, cos φ = 0.85: I = 10000 / (1.732 × 380 × 0.85) = 17.9 A. This is the current on each phase.
What is cos φ and why consider it?
Cos φ (power factor) indicates what fraction of apparent power is active (useful). For resistive loads (heaters, incandescent lamps) cos φ = 1.0. For motors, compressors, transformers — 0.7–0.9. A low cos φ leads to increased current for the same active power.
Why is starting current higher than operating current?
When starting an electric motor, the rotor is stationary and does not generate back-EMF, so the current is limited only by the active resistance of the windings. Starting current is 3–7 times the rated current. For MCB selection, use the operating current, but choose characteristic C or D to avoid tripping during start.
Which MCB to install for a known power?
Calculate the operating current (I = P / (U × cos φ)), then select the nearest standard MCB rating above: 6, 10, 16, 20, 25, 32, 40, 50, 63 A. The MCB rating must not exceed the cable's permissible current. For motors, characteristic C or D.
How to convert kW to kVA and vice versa?
kVA = kW / cos φ. Example: air conditioner 2.5 kW with cos φ = 0.85: 2.5 / 0.85 = 2.94 kVA. Reverse: kW = kVA × cos φ. For heaters and heating elements cos φ = 1.0, so kW = kVA.
How many watts in one volt-ampere?
W = VA × cos φ. At cos φ = 1.0 (heaters): 1 VA = 1 W. At cos φ = 0.85 (motors, air conditioners): 1 VA = 0.85 W. Volt-ampere (VA) is the unit of apparent power, watt (W) is active power.

Related tools

🔌
Cable cross-section calculation
Cable cross-section selection by power, current and installation method per IEC 60364-5-52.
→
🛡
MCB selection by load
Breaker rating and trip curve selection (B/C/D) with coordination and selectivity check.
→
📉
Voltage drop calculator
Voltage drop calculation in cable with visualization and cross-section comparison.
→
← All tools (13)

Calculate MCBs in your panel

ElectroBoard automatically selects MCBs and cables based on entered loads. No manual formulas.

Create a panel for free →