Amps to Watts Converter
Converting amps to watts is essential when you’re working with electrical appliances, wiring circuits, or comparing power ratings. Amps measure current flow whilst watts represent actual power consumption. This converter handles DC circuits, single-phase AC (like your home sockets), and three-phase AC (common in industrial settings).
Quick Conversions (DC at 12V)
Amps to Watts Conversion Chart
These common conversions show how amps translate to watts at standard UK voltages. Domestic circuits typically run at 230V, whilst automotive and marine applications use 12V DC.
| Current (A) | Voltage (V) | Power (W) | Common Application |
|---|---|---|---|
| 1 | 230 | 230 | LED bulb, phone charger |
| 3 | 230 | 690 | Laptop, small TV |
| 5 | 230 | 1,150 | Microwave oven |
| 10 | 230 | 2,300 | Electric heater, kettle |
| 13 | 230 | 2,990 | Maximum UK plug rating |
| 10 | 12 | 120 | Car spotlight |
| 20 | 12 | 240 | Automotive inverter |
| 50 | 400 | 20,000 | Industrial motor (3-phase) |
How the Maths Works
The relationship between amps, volts, and watts comes from Ohm’s Law and basic electrical principles. Here’s how to work it out depending on your circuit type.
DC Circuits
Straightforward multiplication. If you’ve got 5 amps flowing through a 12-volt battery, that’s 5 × 12 = 60 watts.
Single-Phase AC Circuits
AC circuits need power factor because voltage and current don’t always peak at the same time. Most household appliances have a power factor between 0.9 and 1.0. Your kettle pulling 10A at 230V with a power factor of 0.95 consumes 10 × 230 × 0.95 = 2,185 watts.
Three-Phase AC Circuits
Three-phase systems are more efficient for heavy machinery. The √3 factor (approximately 1.732) accounts for the three power lines. A 30A industrial motor running at 400V with a power factor of 0.85 uses 1.732 × 30 × 400 × 0.85 = 17,666 watts.
Worked Examples
Home Appliances
Your washing machine draws 7 amps from a UK socket (230V AC, power factor 0.9). The power consumption is 7 × 230 × 0.9 = 1,449 watts. That’s roughly 1.45 kilowatts per hour when running.
Car Electronics
A car stereo amplifier pulling 15 amps from your 12V battery uses 15 × 12 = 180 watts. This helps you size the correct fuse and wiring gauge.
Workshop Equipment
A three-phase compressor rated at 20A on a 400V supply with power factor 0.88 consumes 1.732 × 20 × 400 × 0.88 = 12,209 watts, or about 12.2 kilowatts.
Why It Matters
Knowing the wattage helps you avoid overloading circuits and tripping breakers. UK ring mains typically handle 32 amps, giving you about 7,360 watts capacity per circuit. If you’re running multiple high-current appliances, you’ll want to spread them across different sockets.
For solar panels and battery systems, this conversion is crucial. A 200-watt solar panel connected to a 12V battery will supply roughly 16.7 amps under ideal conditions (200W ÷ 12V = 16.7A).
What About Power Factor?
Power factor represents how efficiently AC equipment converts current into usable power. Resistive loads like kettles and heaters have a power factor near 1.0. Motors, fluorescent lights, and equipment with transformers typically range from 0.7 to 0.95.
Poor power factor means you’re drawing more current than necessary, which can increase electricity costs for businesses. Most household bills don’t penalise low power factor, but industrial users often face surcharges.
FAQs
Units Of Power Conversions
References
- British Standards Institution. (2016). BS 7671:2018+A2:2022 – Requirements for Electrical Installations. IET Wiring Regulations. London: BSI Standards Limited.
- Electrical Safety First. (2024). Electrical Safety Standards and Guidance for UK Domestic Installations. Retrieved from https://www.electricalsafetyfirst.org.uk/
- International Electrotechnical Commission. (2021). IEC 60050 – International Electrotechnical Vocabulary. Geneva: IEC.
- Energy Saving Trust. (2024). Understanding Your Electricity Consumption. London: Energy Saving Trust.