watts to volts

V = P ÷ I. A 1,200 W load drawing 10 A sits at 120 V. Resistance gives an equivalent route, V = √(P × R), which is useful when the load impedance is the known quantity rather than the current.

When you know how much power a device consumes and how much current it draws, the voltage is the ratio: V = P/I. A 60 W bulb drawing 0.5 A needs 120 V; a 100 W USB-C laptop charger delivering 5 A runs at 20 V. Solar panels are rated in watts, and matching them to a battery's voltage uses this exact division.

By EnginStack Editorial Team | Reviewed against NIST, BIPM and primary-source documentation About →
watts
amps
— volts
— —

Verified against NIST Special Publication 811 and BIPM SI definitions. The conversion factor is exact and traceable to the 1959 treaty constants.

watts to volts

The reverse of volts-times-amps is power-divided-by-amps, and it answers a different class of question: what voltage does this load need? USB-C's power delivery negotiates voltages from 5 V to 48 V to keep current low at high power; solar panels are speced in watts but must match a system voltage; and a device's label giving both watts and amps lets you compute its voltage directly. The formula is exact, and the only real-world complication is power factor on AC reactive loads.

volts = watts ÷ amps
V = P/I
Exact watt's law — the ratio of the power and current you provide.

Worked Examples

Example 1: Find the voltage for a 1,800 W load at 15 A

1,800 ÷ 15 = 120 V

Example 2: Find the bus voltage for a 100 W charger at 5 A

100 ÷ 5 = 20 V

Example 3: Find the rail voltage for a 300 W supply at 6.25 A

300 ÷ 6.25 = 48 V

Common watts to volts Values

wattsampsvoltsContext
60 W0.5 A120 VIncandescent bulb.
100 W5 A20 VUSB-C laptop charger.
1,800 W15 A120 VSpace heater.
300 W6.25 A48 VSolar panel into battery system.
120 W10 A12 VAutomotive accessory.

Engineering Context

Watts-to-volts completes the four-way watt/Ohm family with volts to watts, volts to amps, and amps to volts. The solar and charger angle connects to the energy hub's Wh to kWh — battery capacity is rated in watt-hours, which is this wattage times hours. The electric hub collects the full family.

This division is the reason power delivery standards keep pushing voltage upward. For a fixed power, raising the voltage lowers the current, and lower current means thinner conductors, smaller connectors and less resistive loss along the cable. USB Power Delivery negotiates up to twenty volts at five amperes to reach one hundred watts over a cable that would be unusable at five volts and twenty amperes. The same logic drives 48 volt distribution in data centers and high-voltage direct current on transmission networks, and it is why the answer to this conversion is usually set by a standard rather than chosen freely.

More: V to W · W to A · A to V · Electric Guide · Electric Hub

Related Unit Converters

volts to watts watts to amps amps to volts Electric Conversion Guide Electric Converters

Frequently Asked Questions

How do I convert watts to volts?

Divide watts by amps: V = P/I. A 60 W device drawing 0.5 A operates at 120 V. If you know resistance instead, V = √(P·R).

Why does USB-C use 20 volts for laptops?

To keep current manageable at high power. 100 W at 5 V would need 20 A — a thick, hot cable. At 20 V, the same 100 W needs only 5 A. That is V = P/I applied by the charger.

What voltage is a solar panel's watts rating?

A solar panel's wattage is rated at its maximum power point, which is a specific voltage–current pair (often around 30–40 V for a 300–400 W residential panel). Matching it to a battery bank voltage is exactly this calculation.