How to Convert kW to Amps
Quick answer
- Formula (single-phase):
A = (kW × 1000) ÷ V - 3 kW at 120 V: 25 A
- 7.5 kW at 240 V: 31.25 A
- Voltage is always required, kW and amps are different electrical quantities.
Want the math done for you? Use the kW-to-amps calculator.
kW vs kVA: which one are you working with?
Before converting, it helps to know which rating you have. kW is real power, the actual work done by the circuit, measured in kilowatts. kVA is apparent power, what generators and transformers are typically rated in, which includes reactive components.
For resistive loads like electric heaters, baseboard heating, and water heaters, kW and kVA are essentially the same (power factor = 1). For motors, HVAC compressors, and electronics, kVA is higher than kW. If your nameplate says kW, use this guide. If it says kVA, see How to Convert kVA to Amps.
kW ratings show up most often on appliance nameplates (electric ranges, tankless water heaters, EV chargers) and solar or energy monitoring reports.
The formula
Single-phase: A = (kW × 1000) ÷ V
Where:
- A = current in amps
- kW = real power in kilowatts
- V = voltage in volts
Steps: (1) Find the kW rating, from the nameplate, spec sheet, or by dividing watts by 1000. (2) Identify the system voltage, 120 V or 240 V for most residential US circuits. (3) Multiply kW by 1000, then divide by voltage.
This is the single-phase formula. Three-phase conversions are different and require the square root of 3.
Worked examples
Example 1: Electric water heater (4.5 kW, 240 V)
A tank-style electric water heater rated 4.5 kW at 240 V.
A = (4.5 × 1000) ÷ 240 = 18.75 A
That is close to the limit for a 20 A circuit (with 80% guideline: 16 A sustained). Most water heaters require a dedicated 30 A, 240 V circuit, and a 30 A circuit supports up to 24 A sustained, giving comfortable headroom.
Example 2: Electric range element (3 kW, 240 V)
A single burner element on an electric range rated 3 kW at 240 V.
A = (3 × 1000) ÷ 240 = 12.5 A
Reasonable for a 20 A, 240 V circuit, but a full range runs multiple elements simultaneously and may draw 40–50 A total, which is why ranges typically have 50 A dedicated circuits.
Example 3: Level 2 EV charger (7.2 kW, 240 V)
A home EV charger rated 7.2 kW at 240 V.
A = (7.2 × 1000) ÷ 240 = 30 A
EV charging is a continuous load, it runs for hours at a stretch. The 80% rule means the circuit needs to sustain 30 A, so a 40 A dedicated circuit is the standard recommendation (40 A × 80% = 32 A continuous capacity). If you are comparing EV setups, the EV Charger Amps Calculator and What Wire Size for a Level 2 EV Charger? page keep the next steps in one place.
Reference table: kW to amps at 120 V and 240 V (single-phase)
| kW | Amps at 120 V | Amps at 240 V |
|---|---|---|
| 1 kW | 8.33 A | 4.17 A |
| 2 kW | 16.67 A | 8.33 A |
| 3 kW | 25 A | 12.5 A |
| 4.5 kW | 37.5 A | 18.75 A |
| 7.2 kW | 60 A | 30 A |
| 10 kW | 83.33 A | 41.67 A |
Values assume unity power factor and single-phase. Actual current for loads with reactive components will be higher.
Continuous loads and the 80% rule
Most of the loads where kW ratings matter, water heaters, EV chargers, space heating, are continuous loads. A continuous load is one that runs for three or more hours at a stretch. For continuous loads, the NEC requires the breaker and wiring to be sized at 125% of the load current, which is the same as saying the load should not exceed 80% of the breaker's rated capacity.
Practical example: a 7.2 kW EV charger at 240 V draws 30 A. That is a sustained load, so it needs a circuit rated for at least 30 A ÷ 0.8 = 37.5 A. The next standard breaker size is 40 A, which is why 40 A is the typical recommendation for a 7.2 kW home charger.
Related tools and guides
- kW-to-Amps Calculator, calculate instantly
- EV Charger Amps Calculator, convert charger power into amps and a branch-circuit size
- Amps-to-kW Calculator, reverse direction
- What Wire Size for a Level 2 EV Charger?
- How to Convert kVA to Amps
- How to Convert Watts to Amps
- Electricity Basics
FAQ
Can I convert kW to amps without voltage?
No. kW and amps are different units. Voltage is required to relate them. If you know the circuit is 240 V (common for high-power appliances in the US), use 240 as your voltage. For standard outlets, use 120 V.
My appliance nameplate shows watts, not kW. What do I do?
Divide watts by 1000 to get kW. For example, 4500 W = 4.5 kW. Then apply the formula normally.
What is the difference between kW and kVA for this conversion?
For resistive loads (heaters, water heaters), kW and kVA are the same, so you can use either formula and get the same result. For loads with reactive components (motors, VFDs, some HVAC), kVA is larger than kW. When in doubt, use the kVA rating for circuit sizing, it gives a more conservative (safer) result.
Does this formula apply to three-phase systems?
No. Three-phase single-line calculations use A = (kW × 1000) ÷ (√3 × V × PF). This guide and the kW-to-amps calculator are for single-phase circuits only.
Why do EV chargers and water heaters need dedicated circuits?
Both are high-wattage continuous loads. Continuous loads must be sized at 125% to account for heat buildup in conductors over long run times. Sharing a circuit with other loads means the breaker could trip even within rated limits. Dedicated circuits provide a clean, properly sized path for these loads and reduce nuisance tripping.
Disclaimer: Results are informational estimates for learning and planning only. Always follow the applicable electrical code and consult a qualified licensed electrician for safety-critical work.