Formula
Substituting Ohm's law into power gives:
Watts = volts² / ohms
The wattage page multiplies voltage by current and never asks for resistance. This page never asks for current.
Assumptions
- Resistance is greater than zero.
- The resistor follows Ohm's law at this voltage.
Worked example
12 V across 6 Ω is 24 W.
Input definitions
- Voltage
- The potential difference across the resistance.
- Resistance
- The resistance, in ohms.
Limitations
This is a classroom calculation. It is not a laboratory procedure, a wiring plan, or a measured instrument reading.
Questions
Why can this match the wattage page?
If the current is voltage divided by the same resistance, both formulas describe one circuit. The inputs are different.
Does this size a household circuit?
No. It is the classroom formula for one resistance. It is not a wiring design.