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Use this calculator to

  • Work out the current a heating element draws from its resistance using Ohm's Law
  • Check what a 3 kW appliance pulls on a 230 V circuit before choosing a breaker
  • Confirm a 7.4 kW EV charge point needs a dedicated 32 A supply
  • Verify a plug-in load sits safely under the 13 A limit of a UK socket

Volts to Amps Calculator

Calculate current (A) from voltage (V).

Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Volts to amps sits behind every cable sizing, breaker selection and fault current decision on a commercial site. A new 22 kW EV charger on a 400 V three-phase supply draws around 32 amps per phase at full output. A 50 kW rooftop air-source heat pump on the same supply draws closer to 75 amps. A 250 kVA standby gen-set delivers about 360 amps per phase. Each figure drives a different cable cross-section, a different breaker rating, and a different position on the discrimination ladder. Getting the conversion wrong at design stage propagates through every downstream choice on the panel schedule.

Fault current estimation is the other regular use of the volts to amps maths. The prospective short-circuit current at a distribution board sets the minimum breaking capacity of the protective devices, and it varies sharply with the impedance of the upstream transformer and the cable run back to it. Boards specified against an outdated fault level (the supply infrastructure on UK industrial estates has been quietly upgraded over the last decade) routinely sit underspecified for the actual prospective fault current. A periodic review of the volts to amps figures at the head of the site, against current DNO data, is a worthwhile insurance policy.

Purely Energy works on the procurement and bill side of these projects rather than the panel side, but the cable sizing question is the first place a CFO sees a six-figure capex line on an electrification programme. A clean volts to amps conversion, applied across the new loads being added (EV fleet, heat pump heating, induction kitchens, battery storage), gives a defensible feeder size and a defensible MIC requirement. Both numbers then feed straight into the DNO conversation, the connection cost, and the supply contract structure. Use this tool as the engineering reference; talk to us when the contract gets re-priced.

Common questions

Can I convert volts directly to amps?

No. Voltage alone does not determine current. You also need either the resistance of the load (then I = V / R, Ohm's Law) or the power it draws (then I = P / V). This calculator has a tab for each method; use whichever figure the equipment nameplate or datasheet gives you.

How do I work out amps from volts and resistance?

Ohm's Law: I = V / R. A 46 ohm heating element across a UK 230 V supply draws 230 / 46 = 5 A. Halve the resistance and the current doubles, which is why a partially shorted element trips a breaker: the lower the resistance, the higher the current at a fixed voltage.

How do I work out amps from volts and watts?

Divide power by voltage: I = P / V. A 3 kW immersion heater on a 230 V supply draws 3,000 / 230 = 13.0 A, exactly the limit of a UK 13 A plug, which is why 3 kW is the practical maximum for plug-in appliances. For AC loads with a power factor below 1, divide the result by the power factor as well.

How many amps does a 7.4 kW EV charger draw?

7,400 / 230 = 32.2 A, which is why a 7.4 kW home or workplace charge point sits on a dedicated 32 A single-phase circuit. A 22 kW unit needs a 400 V three-phase supply at about 32 A per phase, calculated with the three-phase formula rather than the single-phase one used here.

Is the UK supply 230 V or 240 V?

The nominal UK single-phase voltage is 230 V with a tolerance of +10% / -6%, so anything from roughly 216 V to 253 V is within specification, and many sites measure around 240 V. Using 230 V in calculations is the standard convention; the difference shifts the current figure by only a few per cent.

Related calculators

The conversions that procurement and engineering use alongside this one.