About this calculator
The Watts to Amps Calculator converts electrical power into current for DC, single-phase AC, and three-phase AC circuits. It is useful for appliance checks, power-supply sizing, rough load estimates, and understanding how wattage relates to current draw.
Watts to Amps Calculator formula
The calculator uses standard electrical relationships between power, voltage, current, resistance, energy, and time. UK mains is commonly 230V single phase at 50Hz, but users should enter the actual values for their circuit, appliance, battery, or tariff.
- DC: I = P / V
- Single phase AC: I = P / (V x PF)
- Three phase AC: I = P / (V x PF x sqrt(3))
How to use the watts to amps calculator
- Enter the known electrical values shown on the appliance label, battery label, circuit design, or energy bill.
- Choose the circuit type, method, unit, cable size, or calculation mode where relevant.
- Use the default UK reference values only as a starting point, not as a substitute for measured or specified values.
- Review the headline result and the secondary outputs such as kW, kWh, cost, voltage drop percentage, or power rating.
- For mains electrical work, use the result as an estimate only and confirm the design with a qualified electrician.
Worked examples
UK kettle
Input: 3,000W at 230V DC/resistive approximation
Calculation: 3,000 / 230
Result: About 13.04A
Three phase motor estimate
Input: 5,000W, 400V, PF 0.8
Calculation: 5,000 / (400 x 0.8 x sqrt(3))
Result: About 9.02A
Electrical calculation notes
Watts measure power at a point in time. Kilowatt-hours measure energy used over time. Amps measure current, volts measure electrical potential difference, and ohms measure resistance.
AC calculations can need power factor and phase assumptions. A resistive heater is different from a motor, compressor, LED driver, or power supply. When the actual power factor is unknown, the calculator default is only an estimate.
UK safety context
- Mains voltage
- UK single-phase mains is commonly treated as 230V at 50Hz. Some appliances and old references may mention 240V.
- Cable and protective devices
- Cable size, breaker size, installation method, grouping, insulation, ambient temperature, and voltage drop all matter in real installations.
- Energy bills
- Electricity costs depend on your own tariff, standing charge, billing days, VAT, and actual metered consumption.
Limitations and safety disclaimer
This calculator is for education and estimation only. It is not electrical design, installation, inspection, compliance, or safety advice.
- Do not use these results as the sole basis for mains wiring or safety-critical design.
- UK electrical work may need to comply with BS 7671 and Part P Building Regulations.
- Battery and airline guidance can change; check airline and official rules before travelling.
- Manufacturer labels, measured values, and professional inspection should override generic assumptions.
Frequently asked questions
Can I use this for UK mains wiring?
Use it only as an estimate. Mains wiring and circuit design should be checked by a qualified electrician.
What voltage should I use in the UK?
UK single-phase mains is commonly treated as 230V. Use the actual measured or specified voltage where precision matters.
What is power factor?
Power factor describes how effectively AC current is converted into useful power. Motors and power supplies often need a power factor assumption.
What is a kWh?
A kilowatt-hour is one kilowatt of power used for one hour. Energy suppliers bill usage in kWh.
Why might real results differ?
Real circuits vary by voltage, temperature, cable route, installation method, appliance duty cycle, and manufacturer design.
Related calculators
- Amps to Watts Calculator
- Volts to Amps Calculator
- Ohm's Law Calculator