Calculator

Free Ohm's Law Calculator

Enter any two known electrical values to solve voltage, current, resistance, and power for a DC or simplified resistive circuit.

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Ohm's Law

Solve voltage, current, resistance, and power when at least two values are known.

VoltageVCurrentAResistanceohmPowerW

Voltage

120 V

Current

5 A

Resistance

24 ohm

Power

600 W

Formula

I = V / R, P = V^2 / R

Voltage, current, resistance, and power

Solve Ohm's Law from any two known values

V = I × R

I = V ÷ R

R = V ÷ I

P = V × I

The calculator also uses P = I²R and P = V²/R when power is one of the known values. Clear any extra fields so exactly the intended pair defines the calculation.

Worked controls examples

These examples show the arithmetic only. Final component and circuit selection still requires the device ratings and installation requirements.

Voltage	Resistance	Current	Power	Example basis
24 V	240 ohm	0.10 A	2.4 W	Small DC control load
24 V	48 ohm	0.50 A	12 W	Higher-current 24 VDC load
5 V	250 ohm	0.020 A	0.10 W	20 mA across a 250 ohm shunt
10 V	500 ohm	0.020 A	0.20 W	20 mA across a 500 ohm shunt

Check the circuit assumptions before using the result

Enter values in volts, amperes, ohms, and watts; convert milliamps to amperes before solving.
Use this relationship for DC or a simplified resistive load. Reactive AC circuits require impedance and phase information.
For a 4-20 mA shunt, confirm the transmitter and input can support the added voltage burden before selecting a resistor.
Check component power rating, tolerance, temperature rise, duty cycle, inrush, manufacturer data, and applicable code requirements separately.

From one calculation to field-ready work

Use the free answer, then choose the depth you need

Ohm's Law stays free for quick voltage, current, resistance, and power checks. Toolkit adds motor, transformer, energy, voltage-drop, wire, and protection workbenches. Pro Toolkit adds complete troubleshooting guides and browser-local field records with PDF output.

4-20 mA shunt resistor guide

Work through 250 and 500 ohm conversions, power, loop burden, tolerance, and input checks.

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Controls engineering boundary

Use this for quick checks on resistive loads, control-circuit current, voltage, and power. Confirm AC impedance, inrush, duty cycle, component ratings, manufacturer data, and applicable code requirements separately.