Ohm's Law Calculator

Ohm’s Law is the foundational relationship in electrical circuit analysis, describing how voltage, current, and resistance interact in a conductor. Named after German physicist Georg Simon Ohm, who published it in 1827, it remains one of the most widely applied equations in all of engineering.

The three forms of Ohm’s Law: V = I × R (Voltage = Current × Resistance) I = V / R (Current = Voltage / Resistance) R = V / I (Resistance = Voltage / Current)

Where:

• V = voltage in volts (V), the “electrical pressure” driving current
• I = current in amperes (A), the flow rate of electric charge
• R = resistance in ohms (Ω), opposition to current flow

Power formulas (derived from Ohm’s Law): P = V × I (Power = Voltage × Current) P = I² × R (Power = Current squared × Resistance) P = V² / R (Power = Voltage squared / Resistance)

Worked examples:

Example 1 — Finding current: A 12V car battery connected to a 6Ω resistor: I = V / R = 12 / 6 = 2 A

Example 2 — Finding resistance: A 120V outlet powering a device drawing 5A: R = V / I = 120 / 5 = 24 Ω

Example 3 — Power dissipation: A resistor with 2A flowing through 10Ω: P = I² × R = 4 × 10 = 40 watts (generates significant heat — resistor must be rated ≥40W)

Real-world applications:

• LED resistor sizing: V_supply − V_LED = I × R → R = (V_supply − V_LED) / I_desired
• Wire gauge selection: higher current needs lower resistance wire to prevent voltage drop and overheating
• Fuse sizing: match fuse amperage to circuit’s maximum design current
• Speaker impedance matching: amplifier output should match speaker impedance (4Ω, 8Ω, 16Ω) for maximum power transfer

Limitation: Ohm’s Law applies to ohmic (linear) conductors at constant temperature. Non-linear components like diodes, transistors, and incandescent bulbs (whose resistance changes with temperature) do not strictly obey it.