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Ohms Law Calculator

Solve voltage, current, resistance and power from two supported known quantities in a DC or purely resistive model.

Your inputs

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EXAMPLE RESULTCalculated locally
Voltage
12 V
Current
2 A
Resistance
6 Ω
Power
24 W
Clear inputs. Transparent methods.
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How it works

A useful distinction

Doubling voltage quadruples resistive power

For an unchanged ideal resistance, twice the voltage gives twice the current and four times the dissipated power. Compare both current and power after changing voltage; proportional voltage changes do not imply proportional heating power.

Choosing two known electrical quantities

Across a 6-ohm resistor, 12 volts gives current 12 ÷ 6 = 2 amperes and power 12 × 2 = 24 watts. Check that the selected pair of known values refers to the same component. Prefixes matter: 6 kilohms is 6,000 ohms, giving 0.002 amperes at the same voltage. This model uses resistive relationships; it does not determine component ratings, safe wiring, or AC behavior involving phase and reactance. Use the resistor tool when first combining a series or parallel network.

Ohm's law: formula and assumptions

V = IR; P = VI = I²R = V²/R.

First and second quantities follow the selected pair. Units are volts, amperes, ohms, and watts. This DC/resistive model does not cover AC impedance.

Ohm’s law with unit prefixes: formula and assumptions

V = I × R and P = V × I.

Two strictly positive known quantities determine the ideal passive resistor solution. Power units distinguish mechanical horsepower and International Table BTU/h.

Worked example

Using the Ohm's law example:

Inputs
Known pair
Voltage & current
First quantity
12
Second quantity
2
Method

V = IR; P = VI = I²R = V²/R.

Result

Example result

Voltage: 12 V

Current: 2 A

Resistance: 6 Ω

Power: 24 W

These are illustrative inputs. Change the values to explore a different scenario.

Formula references

References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.

Common questions

Does Ohm's law mode calculate AC impedance?

No. It uses the DC/resistive relationships V = IR and P = VI, without phase angle or reactive impedance.

In what order should I enter the two known values?

Follow the labels for the selected pair. The first and second quantities change with the chosen relationship.

Prepared by Finflo. See our methodology and editorial policy.