Electrical calculator
Ohm's Law Calculator
Calculate voltage, current, or resistance using Ohm's law.
About the ohm's law calculator
Ohm's law calculator solves for voltage, current, or resistance using the fundamental relationship V = I × R. Enter any two values to find the third, plus power consumption.
How to use this calculator
- 1
Enter two known values
Enter any two of: voltage (V), current (A), or resistance (Ω).
- 2
View results
See the calculated third value plus power in watts.
How the calculation works
V = I × R, I = V ÷ R, R = V ÷ I. Power = V × I.
Example: 12V and 4Ω = 3A and 36W.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about ohm's law calculator
How accurate is the Ohm's law calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.