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Free calculator

Use this calculator to

  • Convert appliance current draw into watts at UK voltages
  • Check how much load a 13 A plug or a 16 A circuit can carry in watts
  • Estimate three-phase machine power from current, voltage and power factor
  • Convert DC currents to watts for solar, battery and vehicle circuits

Amps to Watts Calculator

Convert current (A) to power (W).

A
V
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A
V
PF
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A
V
PF
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Formulas

  • DC: W = A × V
  • AC Single-Phase: W = A × V × PF
  • AC Three-Phase: W = A × V × PF × √3

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Equipment audits and energy reviews work in watts and kWh; the meter readings and engineering surveys arrive in amps. The gap between them is where suppliers' bills go unchallenged and where capex business cases are quietly inflated. A 16 A appliance at 230 V is roughly 3,700 W at unity power factor; if the asset register has it logged as 5 kW the consumption forecast is already 35% high before anyone has switched it on.

For a mid-market business pulling together an ESOS Phase 4 submission or an SECR report, the amps-to-watts conversion is the unit gate every asset has to pass through, and the auditor will trace it back if the numbers do not reconcile. Done in a spreadsheet on five hundred line items it is also where errors compound silently. Spot-checking a handful of high-consumption assets against this calculator is a sensible quality assurance step before the report goes to sign-off and the methodology gets locked.

Purely Energy's bill validation service runs HH and NHH consumption against contracted rates every month for portfolio clients, and the same engineering check sits behind it. When a bill looks wrong, the conversation starts with watts, hours and tariff, and we can usually identify whether the issue is a meter, a misclassification, a CCL reclassification or a genuine consumption change, then take it back to the supplier with the working attached.

Common questions

How do I convert amps to watts?

For DC, multiply current by voltage: W = A x V. For single-phase AC, include the power factor: W = A x V x PF. For three-phase, add the square root of 3: W = A x V x PF x 1.732, using the 400 V line voltage. A 5 A resistive appliance at 230 V is 1,150 W.

How many watts can a UK 13 A plug supply?

At the nominal 230 V, a 13 A plug carries up to 13 x 230 = 2,990 W for a resistive load, which is why 3 kW is the effective ceiling for plug-in appliances such as kettles and heaters in the UK. Anything larger needs a dedicated circuit rather than a standard socket.

What power factor should I enter?

Use 1.0 for purely resistive loads such as heaters, kettles and incandescent lighting. Motors, compressors and drives typically run between 0.8 and 0.9, and the nameplate usually states the value. If you are profiling mixed commercial equipment without nameplate data, 0.9 is a sensible working figure, but confirm it before making sizing decisions.

Why does three-phase use the square root of 3?

In a three-phase system the three currents peak at different moments, 120 degrees apart, so total power is not simply three times one phase measured at line voltage. The mathematics resolves to W = A x V x PF x 1.732 when V is the line-to-line voltage (400 V in the UK). It lets you work from the line current you actually measure.

Is converting amps to watts different for DC circuits?

Yes, it is simpler. DC has no phase angle, so power factor does not apply and W = A x V exactly. A 12 V van or solar circuit carrying 10 A delivers 120 W, and a 48 V battery system discharging 20 A delivers 960 W. The DC tab above applies this directly.

Related calculators

The conversions that procurement and engineering use alongside this one.

Amps to Watts Calculator | Free UK Tool | Purely Energy