Volts to Watts Calculator
Find real power (watts) from voltage using current (amps) for DC and AC (with power factor) or resistance (ohms) for resistive DC via P = V² ÷ R. Volts-first workflow; current mode matches our Amps to Watts Calculator. All calculations run in your browser.
Uses P = V × I (DC) and AC forms with PF — same math as our Amps to Watts Calculator with voltage entered first.
Volts across the load.
DC: load current. AC: RMS line current.
Table of Contents
Why volts alone do not determine watts
Voltage by itself does not fix power in watts. You need either current (with DC vs AC rules and power factor) or, for a resistive model, resistance.
With V and I: P = V × I (DC), P = V × I × PF (single-phase RMS), P = √3 × VL-L × I × PF (balanced three-phase, line-to-line).
With V and R on a resistor: P = V² ÷ R (equivalently V² / R).
This tool complements Amps to Watts (same current-mode physics, volts-first fields) and Watts to Volts for inverse problems.
Formulas
From voltage and current
DC
P (W) = V (V) × I (A)
Real power; no power factor for DC.
AC single-phase
P (W) = VRMS × IRMS × PF
RMS values; PF between 0 and 1.
AC three-phase (balanced)
P (W) = √3 × VL-L × I × PF
Line-to-line RMS voltage. √3 ≈ 1.732.
Resistive DC (voltage and resistance)
P (W) = (V (V))² ÷ R (Ω)
From combining P = V × I with I = V ÷ R. Not for arbitrary AC without a clear resistive model.
Quick Reference Table
| Method | Circuit | Voltage | I or R | PF | Power | Example |
|---|---|---|---|---|---|---|
| V + I | DC | 12 V | 10 A | — | 120 W | P = V × I |
| V + I | AC 1φ | 120 V | 10 A | 0.9 | 1,080 W | Toaster class |
| V + I | AC 3φ | 415 V | 10 A | 0.9 | 6,462 W | VL-L |
| V + R | DC Ω | 24 V | 6 Ω | — | 96 W | 24² ÷ 6 |
FAQ
Yes — identical equations. This page lists voltage first for people who start from volts.
When V is across a resistor R and you want DC power dissipated in that resistor.
Enter volts as a single number (e.g. 0.012 for 12 mV, or 230 for mains RMS).
For balanced real power with line-to-line voltage: P = √3 × VL-L × I × PF.