Ohm law formula tool
Voltage, Current, and Resistance Solver
Solve one Ohm law variable at a time for DC or resistive load notes using voltage, current, and resistance.
Solve Voltage, Current, or Resistance
Calculate V, I, or R from the other two values for basic circuit checks, bench notes, and field documentation.
Result
Voltage
120 V
Result notes
Keep the entered values, assumptions, and result together when adding this calculation to job notes or submittal records. Final installation choices should align with the applicable code edition, equipment listing, manufacturer instructions, local amendments, and AHJ requirements.
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Related charts
Ohm's Law Formula Chart
Use V=IR and power formulas to solve voltage, current, resistance, and watts; 120 V across 24 ohms gives 5 A and 600 W.
Electrical Unit Conversion Chart
Use this electrical unit conversion chart for 500 mA = 0.5 A, 2 kW = 2,000 W, 3 kWh = 3,000 Wh, ohms, uF/F, and calculator checks.
Watts to Amps Chart
Use this watts to amps chart: 1,500W at 120V = 12.5A, 9 kW at 240V = 37.5A; compare 208V, 240V, 480V 3-phase and PF.
Related guides
Ohm's Law Fundamentals for Voltage, Current, Resistance, and Power in U.S. Electrical Work
Use V = I x R and power formulas to solve simple DC and resistive AC checks, review voltage drop, and know when impedance replaces resistance in U.S. electrical troubleshooting.
Ohms Law Formula Guide | V, I, R and Power
Use Ohms Law formulas: 12 V across 4Ω gives 3 A and 36 W; solve V=IR, I=V/R, R=V/I, P=VI, and power wheel examples.
Formula and field context
Solve one Ohm law variable at a time for DC or resistive load notes using voltage, current, and resistance.
Formula context
Ohm's Law Formula Chart
Ohm's Law connects voltage, current, and resistance with V = I x R. Power relationships add P = V x I, P = I^2 x R, and P = V^2 / R. Use this chart as the formula-selection worksheet, then use the calculator result when values, units, and notes need a repeatable record.
Formula
V = I x R, I = V / R, R = V / I, P = V x I, P = I^2 x R, and P = V^2 / R.Variables to keep with the result
- V is voltage in volts.
- I is current in amperes.
- R is resistance in ohms.
- P is real power in watts for the selected circuit condition.
Formula and variables
Ohm law relates voltage, current, and resistance as V = I x R, I = V / R, and R = V / I. Keep the measured or assumed units with the result because volts, amps, and ohms must stay in the same base units for the formula to hold.
Where it fits
This solver is useful when a technician has two known values from a meter reading, nameplate note, resistor value, or low-voltage circuit check and needs the third value. It is a formula worksheet, not a conductor, breaker, or equipment-sizing decision.
Common mistakes
Do not use a simple V/I/R result for reactive AC loads unless impedance has been reduced to an appropriate magnitude. For AC motors, transformers, power factor, and three-phase loads, use the related power, impedance, or motor calculators instead.