Ohm's Law Calculators
Calculate voltage, current, resistance, and power using Ohm's Law and related formulas.
Ohm's Law Calculator
Solve for voltage, current, or resistance using V=IR. Enter any two values to find the third.
Electrical Power Calculator
Calculate electrical power using P=VI, P=I²R, or P=V²/R. Supports all combinations of voltage, current, and resistance.
Voltage Divider Calculator
Calculate output voltage of a resistive voltage divider given R1, R2, and input voltage. Ideal for sensor circuits and bias networks.
Current Divider Calculator
Calculate branch currents when resistors are connected in parallel. Uses the current divider rule.
Series & Parallel Resistance Calculator
Calculate total resistance for resistors in series or parallel combinations. Enter multiple values separated by commas.
Ohm's Law: V = IR
Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it: V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. The law can be rearranged to solve for any of the three quantities: I = V ÷ R (current from voltage and resistance), R = V ÷ I (resistance from voltage and current). Ohm's Law applies to linear (ohmic) conductors at constant temperature. Most metallic conductors are ohmic over a wide range; semiconductors, diodes, and light bulbs are non-ohmic because their resistance changes with current or temperature.
Electrical Power: P = VI
Electrical power is the rate at which energy is transferred: P = V × I (watts = volts × amperes). Combining with Ohm's Law gives two additional forms: P = I²R (power from current and resistance) and P = V²÷R (power from voltage and resistance). These three forms are collectively called the power wheel or PIV triangle. For a 12 V circuit with 2 Ω resistance: I = 12 ÷ 2 = 6 A; P = 12 × 6 = 72 W. Power dissipated in a resistor is converted to heat. This is why wire gauges are rated by maximum current — excessive current causes resistive heating that can melt insulation and start fires.
Voltage Dividers
A voltage divider consists of two resistors in series connected across a supply voltage, with the output taken between them. The output voltage is: Vout = Vin × R2 ÷ (R1 + R2). Voltage dividers are used to produce a reference voltage from a higher supply, to bias transistor base voltages, and to interface sensors with microcontrollers. The Thevenin equivalent resistance of a voltage divider is R1 ∥ R2 (parallel combination). For accurate voltage division, the load resistance should be at least 10× the Thevenin resistance to avoid loading effects that shift the output voltage below the calculated value.
Series and Parallel Resistance
Resistors in series simply add: R_total = R1 + R2 + R3 + ... Current through each resistor is the same; voltage divides proportionally to resistance. Resistors in parallel combine as reciprocals: 1/R_total = 1/R1 + 1/R2 + 1/R3 + ... For two resistors in parallel, the shortcut formula is R_total = (R1 × R2) ÷ (R1 + R2). The total resistance of a parallel combination is always less than the smallest individual resistor. Voltage across each parallel resistor is the same; current divides inversely with resistance. Real circuits often have mixed series-parallel networks that must be simplified step-by-step from the innermost parallel groups outward.