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Electronics · Circuit fundamentals

Calculate V, I, R, and P.

Enter any two known values for one ideal resistive DC component. The calculator derives the other two as you type.

Try the calculator

Free browser-based tool

Enter exactly two known values

Leave the other two fields blank. The example starts with 12 V and 1 kΩ.

Enter volts; for example, 12 (not 12 V).

Enter amperes; 12 mA is 0.012.

Enter ohms; 1 kΩ is 1000.

Enter watts; 144 mW is 0.144.

Calculated values

Voltage (V)
12 V
Current (I)
12 mA
Resistance (R)
1 kΩ
Power (P)
144 mW

This calculator uses ideal DC equations for one ohmic component. It does not model component tolerance, temperature, frequency, nonlinear behavior, source limits, or safe operating area. Check component datasheets and circuit conditions before building or changing hardware.

A practical guide

How the calculator gets the other values

Use two known values to calculate the remaining quantities for one ideal resistive component.

By Amit Kumar Das About the author Published

Relationships used

Ohm’s law relates voltage, current, and resistance: V = I × R. Electrical power is P = V × I. Enter exactly two positive values in base SI units; the tool applies the matching relationships below and displays all four quantities.

Examples of the two known values and the equations used
Known valuesCalculated relationships
Voltage and currentR = V / I, P = V × I
Voltage and resistanceI = V / R, P = V × I
Voltage and powerI = P / V, R = V / I
Current and resistanceV = I × R, P = V × I
Current and powerV = P / I, R = V / I
Resistance and powerI = √(P / R), V = I × R

A checked example: 12 V across 1 kΩ

Enter 12 for voltage and 1000 for resistance. The calculator returns 0.012 A (12 mA) and 0.144 W (144 mW):

I = V / R = 12 / 1000 = 0.012 A
P = V × I = 12 × 0.012 = 0.144 W

The 144 mW calculation is not, by itself, proof that a particular resistor will operate safely. Compare it with the component’s derated power rating and operating conditions; use the Ohm’s law and resistor power lesson for the worked design cautions.

Scope and limitations

  • Use exactly two known fields. Leave the other two empty.
  • Enter positive finite numbers from 1e-12 through 1e12 in base units. Unit suffixes and metric prefixes are not parsed.
  • The relationships assume one ideal, ohmic component under steady DC conditions. They are not a general circuit solver.
  • The result does not account for resistor tolerance, heating, component ratings, reactive components, or nonlinear devices such as diodes.
  • Calculations run in this browser; values are not submitted to TeachyLeaf.

Continue learning with the Ohm’s law tutorial, the voltage-divider lesson, and the resistor color-code calculator.