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DC Voltage–Current Power & Resistance Ratio

Calculate signed DC power and the voltage-to-current ratio at a nonzero operating point.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

At 12 V and 2 A, power is 24 W and the voltage-to-current ratio is 6 Ω.

Power = voltage × current; resistance ratio = voltage/current

Worked example

Enter these known values and leave the other values blank.

Signed voltage
12 V
Signed current
2 A
Voltage-to-current ratio
6 Ω
Signed electrical power
24 W

Assumptions and limitations

  • Voltage and current must be nonzero in the retained model. Use a consistent passive sign convention: positive current enters the positive-voltage terminal.
  • Positive power indicates absorption and negative power indicates delivery under that convention. A negative V/I ratio does not describe an ordinary passive resistor.
  • For a linear passive resistor, V/I is its resistance. For a nonlinear or active element it is an operating-point ratio and need not equal differential resistance.
  • These equations do not calculate average AC power from arbitrary RMS or peak values. The electric-horsepower option uses the 746 W convention.

Common questions

Can the power be negative?

Yes. With the stated sign convention, negative power means the element supplies electrical energy to the circuit.

Does V/I always give the slope of a device’s I–V curve?

No. V/I is a ratio at one point; differential resistance is dV/dI and can differ.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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