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Watts to Amps / Amps to Watts Converter

Convert between watts and amps for single and three-phase circuits

Reference Info & Formulas
Formulas

Single Phase

I = W / (V × PF)

W = V × I × PF

Three Phase

I = W / (√3 × V × PF)

W = √3 × V × I × PF

Quick Reference

60W bulb: 0.26A

100W bulb: 0.43A

2kW heater: 8.70A

3kW kettle: 13.04A

Input
Select direction and enter values
W

Data: Standard electrical formulas (P = V × I × PF)

For guidance only. The responsibility for any electrical installation lies with the qualified person carrying out the work. Always verify calculations independently and apply professional judgement.

How This Calculator Works

Watts and amps are related through voltage — converting between them is one of the most common calculations in electrical work.

For single-phase AC circuits, the relationship is P = V × I × PF, where P is real power in watts, V is voltage, I is current in amps, and PF is the power factor. For purely resistive loads such as heaters, kettles, and incandescent lamps, power factor is 1.0 and watts equal volt-amps. For motors, transformers, and fluorescent lighting, the power factor is less than 1.0 and the current draw is higher than a simple watts ÷ volts calculation would suggest.

Watts = Volts × Amps × Power Factor
V
= Supply voltage (230V single-phase UK)
I
= Current in amps
PF
= Power factor (0–1, 1.0 for resistive loads)

For three-phase circuits, the formula becomes P = √3 × V × I × PF, using the line-to-line voltage of 400V. The calculator handles both single-phase and three-phase conversions automatically.

Quick Reference — Watts to Amps at 230V

Common single-phase conversions (PF = 1.0)

Power (W)Current at 230V (A)Typical Application
5002.2Small heater, iron
1,0004.3Microwave, toaster
2,0008.7Fan heater, kettle
3,00013.0Full-load 13A appliance
5,00021.7Small water heater
7,00030.4Electric shower (low)

Based on 230V nominal supply and power factor of 1.0 (resistive load). For inductive loads, divide by the power factor to get true current.

Practical Notes

Quick Conversion at 230V

Divide watts by 230 for amps, or multiply amps by 230 for watts. For a conservative estimate when checking cable and MCB capacity, divide watts by 250 instead — this gives a slightly higher current figure and builds in a margin for voltage variation.

Power Factor for Inductive Loads

Always account for power factor when converting for motor or inductive loads. Ignoring it underestimates the current draw, which can lead to undersized cables and nuisance MCB tripping. A motor rated at 2kW with a PF of 0.8 actually draws 10.9A, not 8.7A.

Continuous vs Intermittent Loads

For loads that run continuously (more than 30 minutes), size the circuit for the full rated current with no reduction. Appliances such as storage heaters, immersion heaters, and EV chargers are continuous loads. The cable and protective device must be rated for 100% of the design current without relying on thermal cycling.

Frequently Asked Questions

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