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Free calculator

Use this calculator to

  • Find the voltage across a component from current and resistance using Ohm's law
  • Estimate the voltage drop along a cable run from its resistance and load current
  • Work out an operating voltage from a load's power rating and measured current
  • Cross-check meter readings when two of voltage, current and power are known

Amps to Volts Calculator

Calculate voltage (V) from current (A) using resistance or power.

A
Ω
Result
—
A
W
Result
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Formulas

  • V = I × R (Ohm's Law)
  • V = P / I

Related Calculators

V→A

Volts to Amps

Convert voltage (V) to current (A)

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A→kVA

Amps to kVA

Convert current (A) to apparent power (kVA)

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A→kW

Amps to kW

Convert current (A) to real power (kW)

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Common scenarios

Select one to run it in the calculator above.

For business

Why this matters for businesses

Low-voltage circuits cover more of a commercial estate than most operations teams realise: signage, emergency lighting, access control, CCTV, point-of-sale terminals, EPOS power-over-Ethernet networks, comms cabinets and door-entry systems. Each item is trivial on its own, but a multi-site retail group can be running tens of thousands of these end-points across hundreds of stores. The cumulative quiet load is rarely on anyone's radar until a refurbishment forces an audit, or until a section of the estate starts tripping intermittently and the maintenance bill spikes.

Getting the voltage right matters for safety, for selector switching, and for the bill. A drop of 5 V on a long run at the wrong gauge of cable is the difference between rated output and underperforming kit, and the cost shows up as flickering signage, premature LED failures, or HVAC controls cycling more than they should. Verifying voltage against measured current and known resistance is the cheapest diagnostic available.

Purely Energy works with multi-site retail, hospitality and commercial property groups where the low-voltage estate is the long tail of consumption rather than the headline load. We baseline kWh by site through Purely Insights so the maintenance team can see when a circuit is drifting outside its expected envelope, which is usually weeks before the failure that triggers the call-out, and the same dashboard lines up the energy savings against the bill the FD signs off every month.

Common questions

How do I calculate volts from amps?

You need one more quantity. With resistance, use Ohm's law: V = I x R, so 5 A through a 46 ohm element gives 230 V. With power, use V = P / I, so a 3,000 W load drawing 13 A is running at about 230.8 V. The two tabs above cover both routes.

Can I convert amps directly to volts?

No. Amps measure current flow and volts measure electrical potential, so there is no fixed conversion between them. The relationship depends on the circuit: either its resistance (V = I x R) or the power being delivered (V = P / I). That is why this calculator asks for resistance or power alongside the current.

How does V = I x R help with cable voltage drop?

Current flowing through a cable's own resistance loses voltage along the run: drop = I x R, so 10 A through 0.5 ohm of conductor resistance loses 5 V. UK wiring practice under BS 7671 recommends keeping the drop within 3 percent of nominal voltage for lighting and 5 percent for other uses, so long runs at high current need larger conductors.

What is Ohm's law?

Ohm's law states that the voltage across a conductor equals the current through it multiplied by its resistance: V = I x R. It can be rearranged to find any of the three quantities, I = V / R or R = V / I, and it underpins almost every circuit calculation, from sizing a resistor to estimating fault currents and cable losses.

Which tab should I use, resistance or power?

Use the resistance tab when you know the ohmic value of the component or cable, which suits voltage drop and component-level calculations. Use the power tab when you know a load's wattage from its nameplate and have measured its current with a clamp meter: V = P / I then reveals the voltage at the load terminals.

Related calculators

The conversions that procurement and engineering use alongside this one.

Amps to Volts Calculator | Free UK Tool | Purely Energy